diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java b/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java
index 536e8271a..8db4c8d03 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java
@@ -743,7 +743,7 @@ public class WhisperServerService extends Application<WhisperServerConfiguration
 
     final AccountAuthenticator accountAuthenticator = new AccountAuthenticator(accountsManager);
 
-    final MessageSender messageSender = new MessageSender(messagesManager, pushNotificationManager);
+    final MessageSender messageSender = new MessageSender(messagesManager, pushNotificationManager, dynamicConfigurationManager);
     final ReceiptSender receiptSender = new ReceiptSender(accountsManager, messageSender, receiptSenderExecutor);
     final CloudflareTurnCredentialsManager cloudflareTurnCredentialsManager = new CloudflareTurnCredentialsManager(
         config.getTurnConfiguration().cloudflare().apiToken().value(),
diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/configuration/dynamic/DynamicConfiguration.java b/service/src/main/java/org/whispersystems/textsecuregcm/configuration/dynamic/DynamicConfiguration.java
index e8313c9c3..2a9b90bfe 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/configuration/dynamic/DynamicConfiguration.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/configuration/dynamic/DynamicConfiguration.java
@@ -12,7 +12,6 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
-import org.signal.chat.calling.GetTurnCredentialsResponseOrBuilder;
 import org.whispersystems.textsecuregcm.limits.RateLimiterConfig;
 
 public class DynamicConfiguration {
@@ -45,6 +44,10 @@ public class DynamicConfiguration {
   @Valid
   DynamicMessagePersisterConfiguration messagePersister = new DynamicMessagePersisterConfiguration();
 
+  @JsonProperty
+  @Valid
+  DynamicMessageDeliveryConfiguration messageDelivery = new DynamicMessageDeliveryConfiguration();
+
   @JsonProperty
   @Valid
   DynamicRegistrationConfiguration registrationConfiguration = new DynamicRegistrationConfiguration(false);
@@ -111,6 +114,10 @@ public class DynamicConfiguration {
     return messagePersister;
   }
 
+  public DynamicMessageDeliveryConfiguration getMessageDeliveryConfiguration() {
+    return messageDelivery;
+  }
+
   public DynamicRegistrationConfiguration getRegistrationConfiguration() {
     return registrationConfiguration;
   }
diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/configuration/dynamic/DynamicMessageDeliveryConfiguration.java b/service/src/main/java/org/whispersystems/textsecuregcm/configuration/dynamic/DynamicMessageDeliveryConfiguration.java
new file mode 100644
index 000000000..83e415caf
--- /dev/null
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/configuration/dynamic/DynamicMessageDeliveryConfiguration.java
@@ -0,0 +1,18 @@
+/*
+ * Copyright 2026 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.whispersystems.textsecuregcm.configuration.dynamic;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+public class DynamicMessageDeliveryConfiguration {
+
+  @JsonProperty
+  private boolean readOnly = false;
+
+  public boolean isReadOnly() {
+    return readOnly;
+  }
+}
diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/controllers/AccountControllerV2.java b/service/src/main/java/org/whispersystems/textsecuregcm/controllers/AccountControllerV2.java
index 0b9dec6ef..99b702207 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/controllers/AccountControllerV2.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/controllers/AccountControllerV2.java
@@ -22,6 +22,7 @@ import jakarta.ws.rs.HeaderParam;
 import jakarta.ws.rs.PUT;
 import jakarta.ws.rs.Path;
 import jakarta.ws.rs.Produces;
+import jakarta.ws.rs.ServiceUnavailableException;
 import jakarta.ws.rs.WebApplicationException;
 import jakarta.ws.rs.container.ContainerRequestContext;
 import jakarta.ws.rs.core.Context;
@@ -121,6 +122,8 @@ public class AccountControllerV2 {
       throw new BadRequestException(e);
     } catch (final MessageTooLargeException e) {
       throw new WebApplicationException(Response.Status.REQUEST_ENTITY_TOO_LARGE);
+    } catch (final MessageDeliveryNotAllowedException e) {
+      throw new ServiceUnavailableException();
     }
   }
 
diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/controllers/MessageController.java b/service/src/main/java/org/whispersystems/textsecuregcm/controllers/MessageController.java
index c8121abc5..4712baf53 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/controllers/MessageController.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/controllers/MessageController.java
@@ -33,6 +33,7 @@ import jakarta.ws.rs.Path;
 import jakarta.ws.rs.PathParam;
 import jakarta.ws.rs.Produces;
 import jakarta.ws.rs.QueryParam;
+import jakarta.ws.rs.ServiceUnavailableException;
 import jakarta.ws.rs.WebApplicationException;
 import jakarta.ws.rs.container.ContainerRequestContext;
 import jakarta.ws.rs.core.Context;
@@ -471,6 +472,8 @@ public class MessageController {
       }
     } catch (final MessageTooLargeException e) {
       throw new WebApplicationException(Status.REQUEST_ENTITY_TOO_LARGE);
+    } catch (final MessageDeliveryNotAllowedException e) {
+      throw new ServiceUnavailableException();
     }
   }
 
@@ -724,6 +727,8 @@ public class MessageController {
           .type(MediaType.APPLICATION_JSON)
           .entity(accountStaleDevices)
           .build());
+    } catch (final MessageDeliveryNotAllowedException e) {
+      throw new ServiceUnavailableException();
     }
   }
 
diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/controllers/MessageDeliveryNotAllowedException.java b/service/src/main/java/org/whispersystems/textsecuregcm/controllers/MessageDeliveryNotAllowedException.java
new file mode 100644
index 000000000..6c6ee3ceb
--- /dev/null
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/controllers/MessageDeliveryNotAllowedException.java
@@ -0,0 +1,11 @@
+/*
+ * Copyright 2026 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.whispersystems.textsecuregcm.controllers;
+
+import org.whispersystems.textsecuregcm.util.NoStackTraceException;
+
+public class MessageDeliveryNotAllowedException extends NoStackTraceException {
+}
diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/grpc/GrpcExceptions.java b/service/src/main/java/org/whispersystems/textsecuregcm/grpc/GrpcExceptions.java
index 4a82aef20..2cc7b4350 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/grpc/GrpcExceptions.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/grpc/GrpcExceptions.java
@@ -158,6 +158,10 @@ public class GrpcExceptions {
     return StatusProto.toStatusRuntimeException(builder.build());
   }
 
+  public static StatusRuntimeException unavailable() {
+    return unavailable(null);
+  }
+
   /// There was an internal error processing the RPC. The client should retry the request with exponential backoff.
   ///
   /// @return A [StatusRuntimeException] encoding the error
diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/grpc/MessagesAnonymousGrpcService.java b/service/src/main/java/org/whispersystems/textsecuregcm/grpc/MessagesAnonymousGrpcService.java
index a4a91ba2b..457be793e 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/grpc/MessagesAnonymousGrpcService.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/grpc/MessagesAnonymousGrpcService.java
@@ -11,6 +11,7 @@ import java.util.Map;
 import java.util.Optional;
 import java.util.stream.Collectors;
 import com.google.protobuf.Empty;
+import io.grpc.Status;
 import org.signal.chat.errors.FailedUnidentifiedAuthorization;
 import org.signal.chat.errors.NotFound;
 import org.signal.chat.messages.IndividualRecipientMessageBundle;
@@ -28,6 +29,7 @@ import org.signal.libsignal.protocol.InvalidMessageException;
 import org.signal.libsignal.protocol.InvalidVersionException;
 import org.signal.libsignal.protocol.SealedSenderMultiRecipientMessage;
 import org.whispersystems.textsecuregcm.auth.UnidentifiedAccessUtil;
+import org.whispersystems.textsecuregcm.controllers.MessageDeliveryNotAllowedException;
 import org.whispersystems.textsecuregcm.controllers.MismatchedDevicesException;
 import org.whispersystems.textsecuregcm.controllers.MultiRecipientMismatchedDevicesException;
 import org.whispersystems.textsecuregcm.controllers.RateLimitExceededException;
@@ -229,6 +231,8 @@ public class MessagesAnonymousGrpcService extends SimpleMessagesAnonymousGrpc.Me
           .build();
     } catch (final MessageTooLargeException e) {
       throw GrpcExceptions.invalidArguments("message too large");
+    } catch (final MessageDeliveryNotAllowedException e) {
+      throw GrpcExceptions.unavailable();
     }
   }
 
@@ -325,6 +329,8 @@ public class MessagesAnonymousGrpcService extends SimpleMessagesAnonymousGrpc.Me
       return SendMultiRecipientMessageResponse.newBuilder()
           .setMismatchedDevices(mismatchedDevicesBuilder)
           .build();
+    } catch (final MessageDeliveryNotAllowedException e) {
+      throw GrpcExceptions.unavailable();
     }
   }
 
diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/grpc/MessagesGrpcService.java b/service/src/main/java/org/whispersystems/textsecuregcm/grpc/MessagesGrpcService.java
index a8ad18228..124302def 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/grpc/MessagesGrpcService.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/grpc/MessagesGrpcService.java
@@ -5,21 +5,24 @@
 
 package org.whispersystems.textsecuregcm.grpc;
 
+import static org.whispersystems.textsecuregcm.grpc.MessagesGrpcHelper.buildMismatchedDevices;
+
 import com.google.protobuf.ByteString;
+import com.google.protobuf.Empty;
 import java.time.Clock;
 import java.util.Map;
 import java.util.Optional;
 import java.util.stream.Collectors;
-import com.google.protobuf.Empty;
 import org.signal.chat.errors.NotFound;
-import org.signal.chat.messages.SendMessageType;
 import org.signal.chat.messages.IndividualRecipientMessageBundle;
 import org.signal.chat.messages.SendAuthenticatedSenderMessageRequest;
 import org.signal.chat.messages.SendMessageAuthenticatedSenderResponse;
+import org.signal.chat.messages.SendMessageType;
 import org.signal.chat.messages.SendSyncMessageRequest;
 import org.signal.chat.messages.SimpleMessagesGrpc;
 import org.whispersystems.textsecuregcm.auth.grpc.AuthenticatedDevice;
 import org.whispersystems.textsecuregcm.auth.grpc.AuthenticationUtil;
+import org.whispersystems.textsecuregcm.controllers.MessageDeliveryNotAllowedException;
 import org.whispersystems.textsecuregcm.controllers.MismatchedDevicesException;
 import org.whispersystems.textsecuregcm.controllers.RateLimitExceededException;
 import org.whispersystems.textsecuregcm.entities.MessageProtos;
@@ -36,8 +39,6 @@ import org.whispersystems.textsecuregcm.spam.SpamChecker;
 import org.whispersystems.textsecuregcm.storage.Account;
 import org.whispersystems.textsecuregcm.storage.AccountsManager;
 
-import static org.whispersystems.textsecuregcm.grpc.MessagesGrpcHelper.buildMismatchedDevices;
-
 public class MessagesGrpcService extends SimpleMessagesGrpc.MessagesImplBase {
 
   private final AccountsManager accountsManager;
@@ -192,6 +193,8 @@ public class MessagesGrpcService extends SimpleMessagesGrpc.MessagesImplBase {
           .build();
     } catch (final MessageTooLargeException e) {
       throw GrpcExceptions.invalidArguments("message too large");
+    } catch (final MessageDeliveryNotAllowedException e) {
+      throw GrpcExceptions.unavailable();
     }
   }
 
diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/push/MessageSender.java b/service/src/main/java/org/whispersystems/textsecuregcm/push/MessageSender.java
index 08486fd94..11497997d 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/push/MessageSender.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/push/MessageSender.java
@@ -26,6 +26,8 @@ import javax.annotation.Nullable;
 import kotlin.Pair;
 import org.apache.commons.lang3.StringUtils;
 import org.signal.libsignal.protocol.SealedSenderMultiRecipientMessage;
+import org.whispersystems.textsecuregcm.configuration.dynamic.DynamicConfiguration;
+import org.whispersystems.textsecuregcm.controllers.MessageDeliveryNotAllowedException;
 import org.whispersystems.textsecuregcm.controllers.MismatchedDevices;
 import org.whispersystems.textsecuregcm.controllers.MismatchedDevicesException;
 import org.whispersystems.textsecuregcm.controllers.MultiRecipientMismatchedDevicesException;
@@ -36,6 +38,7 @@ import org.whispersystems.textsecuregcm.metrics.UserAgentTagUtil;
 import org.whispersystems.textsecuregcm.spam.MessageDeliveryListener;
 import org.whispersystems.textsecuregcm.storage.Account;
 import org.whispersystems.textsecuregcm.storage.Device;
+import org.whispersystems.textsecuregcm.storage.DynamicConfigurationManager;
 import org.whispersystems.textsecuregcm.storage.MessagesManager;
 import org.whispersystems.textsecuregcm.util.Util;
 
@@ -54,6 +57,7 @@ public class MessageSender {
 
   private final MessagesManager messagesManager;
   private final PushNotificationManager pushNotificationManager;
+  private final DynamicConfigurationManager<DynamicConfiguration> dynamicConfigurationManager;
 
   private final List<MessageDeliveryListener> messageDeliveryListeners = new ArrayList<>();
 
@@ -80,9 +84,12 @@ public class MessageSender {
   @VisibleForTesting
   static final byte NO_EXCLUDED_DEVICE_ID = -1;
 
-  public MessageSender(final MessagesManager messagesManager, final PushNotificationManager pushNotificationManager) {
+  public MessageSender(final MessagesManager messagesManager,
+      final PushNotificationManager pushNotificationManager,
+      final DynamicConfigurationManager<DynamicConfiguration> dynamicConfigurationManager) {
     this.messagesManager = messagesManager;
     this.pushNotificationManager = pushNotificationManager;
+    this.dynamicConfigurationManager = dynamicConfigurationManager;
   }
 
   public void addMessageDeliveryListener(final MessageDeliveryListener messageDeliveryListener) {
@@ -112,7 +119,12 @@ public class MessageSender {
       final Map<Byte, Envelope> messagesByDeviceId,
       final Map<Byte, Integer> registrationIdsByDeviceId,
       @SuppressWarnings("OptionalUsedAsFieldOrParameterType") final Optional<Byte> syncMessageSenderDeviceId,
-      @Nullable final String userAgent) throws MismatchedDevicesException, MessageTooLargeException {
+      @Nullable final String userAgent)
+      throws MismatchedDevicesException, MessageTooLargeException, MessageDeliveryNotAllowedException {
+
+    if (dynamicConfigurationManager.getConfiguration().getMessageDeliveryConfiguration().isReadOnly()) {
+      throw new MessageDeliveryNotAllowedException();
+    }
 
     final Tag platformTag = UserAgentTagUtil.getPlatformTag(userAgent);
 
@@ -189,7 +201,12 @@ public class MessageSender {
       final boolean isStory,
       final boolean isEphemeral,
       final boolean isUrgent,
-      @Nullable final String userAgent) throws MultiRecipientMismatchedDevicesException, MessageTooLargeException {
+      @Nullable final String userAgent)
+      throws MultiRecipientMismatchedDevicesException, MessageTooLargeException, MessageDeliveryNotAllowedException {
+
+    if (dynamicConfigurationManager.getConfiguration().getMessageDeliveryConfiguration().isReadOnly()) {
+      throw new MessageDeliveryNotAllowedException();
+    }
 
     final Tag platformTag = UserAgentTagUtil.getPlatformTag(userAgent);
 
diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/storage/ChangeNumberManager.java b/service/src/main/java/org/whispersystems/textsecuregcm/storage/ChangeNumberManager.java
index 0756d8013..9f9e28b1b 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/storage/ChangeNumberManager.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/storage/ChangeNumberManager.java
@@ -21,6 +21,7 @@ import org.slf4j.LoggerFactory;
 import org.whispersystems.textsecuregcm.auth.PhoneVerificationTokenManager;
 import org.whispersystems.textsecuregcm.auth.RegistrationLockVerificationManager;
 import org.whispersystems.textsecuregcm.controllers.AccountControllerV2;
+import org.whispersystems.textsecuregcm.controllers.MessageDeliveryNotAllowedException;
 import org.whispersystems.textsecuregcm.controllers.MismatchedDevicesException;
 import org.whispersystems.textsecuregcm.controllers.RateLimitExceededException;
 import org.whispersystems.textsecuregcm.entities.ECSignedPreKey;
@@ -81,7 +82,7 @@ public class ChangeNumberManager {
       final List<IncomingMessage> deviceMessages,
       final Map<Byte, Integer> pniRegistrationIds,
       final ContainerRequestContext containerRequestContext)
-      throws InterruptedException, MismatchedDevicesException, MessageTooLargeException, RateLimitExceededException {
+      throws InterruptedException, MismatchedDevicesException, MessageTooLargeException, RateLimitExceededException, MessageDeliveryNotAllowedException {
 
     final String senderUserAgent = containerRequestContext.getHeaderString(HttpHeaders.USER_AGENT);
 
diff --git a/service/src/test/java/org/whispersystems/textsecuregcm/controllers/AccountControllerV2Test.java b/service/src/test/java/org/whispersystems/textsecuregcm/controllers/AccountControllerV2Test.java
index b72c62f7b..0ca886d1f 100644
--- a/service/src/test/java/org/whispersystems/textsecuregcm/controllers/AccountControllerV2Test.java
+++ b/service/src/test/java/org/whispersystems/textsecuregcm/controllers/AccountControllerV2Test.java
@@ -292,7 +292,7 @@ class AccountControllerV2Test {
     @ParameterizedTest
     @MethodSource
     void phoneVerificationException(final Exception exception, final int expectedStatus)
-        throws InterruptedException, MessageTooLargeException, MismatchedDevicesException, RateLimitExceededException {
+        throws InterruptedException, MessageTooLargeException, MismatchedDevicesException, RateLimitExceededException, MessageDeliveryNotAllowedException {
       doThrow(exception)
           .when(changeNumberManager).changeNumber(any(), any(), any(), any(), any(), any(), any(), any(), any(), any(), any());
 
@@ -338,6 +338,28 @@ class AccountControllerV2Test {
       }
     }
 
+    @Test
+    void messageDeliveryNotAllowed() throws Exception {
+      doThrow(MessageDeliveryNotAllowedException.class)
+          .when(changeNumberManager).changeNumber(any(), any(), any(), any(), any(), any(), any(), any(), any(), any(), any());
+
+      try (final Response response = resources.getJerseyTest()
+          .target("/v2/accounts/number")
+          .request()
+          .header(HttpHeaders.AUTHORIZATION,
+              AuthHelper.getAuthHeader(AuthHelper.VALID_UUID, AuthHelper.VALID_PASSWORD))
+          .put(Entity.entity(
+              new ChangeNumberRequest(encodeSessionId("session"), null, NEW_NUMBER, "123", IDENTITY_KEY,
+                  Collections.emptyList(),
+                  Map.of(Device.PRIMARY_ID, KeysHelper.signedECPreKey(1, IDENTITY_KEY_PAIR)),
+                  Map.of(Device.PRIMARY_ID, KeysHelper.signedKEMPreKey(2, IDENTITY_KEY_PAIR)),
+                  Map.of(Device.PRIMARY_ID, 17)),
+              MediaType.APPLICATION_JSON_TYPE))) {
+
+        assertEquals(503, response.getStatus());
+      }
+    }
+
     /**
      * Valid request JSON with the given Recovery Password
      */
diff --git a/service/src/test/java/org/whispersystems/textsecuregcm/controllers/MessageControllerTest.java b/service/src/test/java/org/whispersystems/textsecuregcm/controllers/MessageControllerTest.java
index bb17988a6..a4d4308cc 100644
--- a/service/src/test/java/org/whispersystems/textsecuregcm/controllers/MessageControllerTest.java
+++ b/service/src/test/java/org/whispersystems/textsecuregcm/controllers/MessageControllerTest.java
@@ -196,7 +196,8 @@ class MessageControllerTest {
       .build();
 
   @BeforeEach
-  void setup() throws MultiRecipientMismatchedDevicesException, MessageTooLargeException {
+  void setup()
+      throws MultiRecipientMismatchedDevicesException, MessageTooLargeException, MessageDeliveryNotAllowedException {
     reset(pushNotificationScheduler);
 
     when(messageSender.sendMultiRecipientMessage(any(), any(), anyLong(), anyBoolean(), anyBoolean(), anyBoolean(), any()))
@@ -545,6 +546,24 @@ class MessageControllerTest {
     }
   }
 
+  @Test
+  void testSingleDeviceMessageDeliveryNotAllowed() throws Exception {
+    doThrow(MessageDeliveryNotAllowedException.class)
+        .when(messageSender).sendMessages(any(), any(), any(), any(), any(), any());
+
+    try (final Response response =
+        resources.getJerseyTest()
+            .target(String.format("/v1/messages/%s", SINGLE_DEVICE_UUID))
+            .request()
+            .header("Authorization", AuthHelper.getAuthHeader(AuthHelper.VALID_UUID, AuthHelper.VALID_PASSWORD))
+            .put(Entity.entity(SystemMapper.jsonMapper().readValue(jsonFixture("fixtures/current_message_single_device.json"),
+                    IncomingMessageList.class),
+                MediaType.APPLICATION_JSON_TYPE))) {
+
+      assertThat(response.getStatus(), is(equalTo(503)));
+    }
+  }
+
   @Test
   void testSendBadAuth() throws Exception {
     try (final Response response =
@@ -1042,7 +1061,8 @@ class MessageControllerTest {
   }
 
   @Test
-  void testValidateContentLength() throws MismatchedDevicesException, MessageTooLargeException, IOException {
+  void testValidateContentLength()
+      throws MismatchedDevicesException, MessageTooLargeException, IOException, MessageDeliveryNotAllowedException {
     doThrow(new MessageTooLargeException()).when(messageSender).sendMessages(any(), any(), any(), any(), any(), any());
 
     try (final Response response =
@@ -1101,7 +1121,7 @@ class MessageControllerTest {
       final Set<Account> expectedResolvedAccounts,
       final Set<ServiceIdentifier> expectedUuids404,
       @Nullable final MultiRecipientMismatchedDevicesException mismatchedDevicesException)
-      throws MultiRecipientMismatchedDevicesException, MessageTooLargeException {
+      throws MultiRecipientMismatchedDevicesException, MessageTooLargeException, MessageDeliveryNotAllowedException {
 
     clock.pin(START_OF_DAY);
 
@@ -1674,6 +1694,72 @@ class MessageControllerTest {
     }
   }
 
+  @Test
+  void sendMultiRecipientMessageMessageDeliveryNotAllowed() throws Exception {
+
+    clock.pin(START_OF_DAY);
+
+    final UUID singleDeviceAccountAci = UUID.randomUUID();
+    final UUID singleDeviceAccountPni = UUID.randomUUID();
+
+    final byte[] singleDeviceAccountUak = TestRandomUtil.nextBytes(UnidentifiedAccessUtil.UNIDENTIFIED_ACCESS_KEY_LENGTH);
+
+    final int singleDevicePrimaryRegistrationId = 1;
+
+    final Device singleDeviceAccountPrimary = mock(Device.class);
+    when(singleDeviceAccountPrimary.getId()).thenReturn(Device.PRIMARY_ID);
+    when(singleDeviceAccountPrimary.getRegistrationId(IdentityType.ACI)).thenReturn(singleDevicePrimaryRegistrationId);
+
+    final Account singleDeviceAccount = mock(Account.class);
+    when(singleDeviceAccount.getIdentifier(IdentityType.ACI)).thenReturn(singleDeviceAccountAci);
+    when(singleDeviceAccount.getUnidentifiedAccessKey()).thenReturn(Optional.of(singleDeviceAccountUak));
+    when(singleDeviceAccount.getDevices()).thenReturn(List.of(singleDeviceAccountPrimary));
+    when(singleDeviceAccount.getDevice(anyByte())).thenReturn(Optional.empty());
+    when(singleDeviceAccount.getDevice(Device.PRIMARY_ID)).thenReturn(Optional.of(singleDeviceAccountPrimary));
+
+    final Map<ServiceIdentifier, Account> accountsByServiceIdentifier = Map.of(
+        new AciServiceIdentifier(singleDeviceAccountAci), singleDeviceAccount,
+        new PniServiceIdentifier(singleDeviceAccountPni), singleDeviceAccount);
+
+    final byte[] aciMessage = MultiRecipientMessageHelper.generateMultiRecipientMessage(List.of(
+        new TestRecipient(new AciServiceIdentifier(singleDeviceAccountAci), Device.PRIMARY_ID, singleDevicePrimaryRegistrationId, new byte[48])));
+
+    when(accountsManager.getByServiceIdentifierAsync(any()))
+        .thenReturn(CompletableFuture.completedFuture(Optional.empty()));
+
+    accountsByServiceIdentifier.forEach(((serviceIdentifier, account) ->
+        when(accountsManager.getByServiceIdentifierAsync(serviceIdentifier))
+            .thenReturn(CompletableFuture.completedFuture(Optional.of(account)))));
+
+    final boolean ephemeral = true;
+    final boolean urgent = false;
+    final boolean story = false;
+
+    final Invocation.Builder invocationBuilder = resources
+        .getJerseyTest()
+        .target("/v1/messages/multi_recipient")
+        .queryParam("ts", clock.millis())
+        .queryParam("online", ephemeral)
+        .queryParam("story", story)
+        .queryParam("urgent", urgent)
+        .request()
+        .header(HeaderUtils.GROUP_SEND_TOKEN, AuthHelper.validGroupSendTokenHeader(serverSecretParams,
+            List.of(new AciServiceIdentifier(singleDeviceAccountAci)),
+            START_OF_DAY.plus(Duration.ofDays(1))));
+
+    when(rateLimiter.validateAsync(any(UUID.class)))
+        .thenReturn(CompletableFuture.completedFuture(null));
+
+    doThrow(MessageDeliveryNotAllowedException.class)
+        .when(messageSender).sendMultiRecipientMessage(any(), any(), anyLong(), anyBoolean(), anyBoolean(), anyBoolean(), any());
+
+    try (final Response response = invocationBuilder
+        .put(Entity.entity(aciMessage, MultiRecipientMessageProvider.MEDIA_TYPE))) {
+
+      assertThat(response.getStatus(), is(equalTo(503)));
+    }
+  }
+
   @SuppressWarnings("SameParameterValue")
   private static Envelope generateEnvelope(UUID guid, int type, long timestamp, UUID sourceUuid,
       byte sourceDevice, UUID destinationUuid, UUID updatedPni, byte[] content, long serverTimestamp) {
diff --git a/service/src/test/java/org/whispersystems/textsecuregcm/grpc/MessagesAnonymousGrpcServiceTest.java b/service/src/test/java/org/whispersystems/textsecuregcm/grpc/MessagesAnonymousGrpcServiceTest.java
index b91bbb877..6e860b12a 100644
--- a/service/src/test/java/org/whispersystems/textsecuregcm/grpc/MessagesAnonymousGrpcServiceTest.java
+++ b/service/src/test/java/org/whispersystems/textsecuregcm/grpc/MessagesAnonymousGrpcServiceTest.java
@@ -54,6 +54,7 @@ import org.signal.chat.messages.SendMultiRecipientStoryRequest;
 import org.signal.chat.messages.SendSealedSenderMessageRequest;
 import org.signal.chat.messages.SendStoryMessageRequest;
 import org.whispersystems.textsecuregcm.auth.UnidentifiedAccessUtil;
+import org.whispersystems.textsecuregcm.controllers.MessageDeliveryNotAllowedException;
 import org.whispersystems.textsecuregcm.controllers.MismatchedDevicesException;
 import org.whispersystems.textsecuregcm.controllers.MultiRecipientMismatchedDevicesException;
 import org.whispersystems.textsecuregcm.controllers.RateLimitExceededException;
@@ -156,7 +157,7 @@ class MessagesAnonymousGrpcServiceTest extends
         @CartesianTest.Values(booleans = {true, false}) final boolean ephemeral,
         @CartesianTest.Values(booleans = {true, false}) final boolean urgent,
         @CartesianTest.Values(booleans = {true, false}) final boolean includeReportSpamToken)
-        throws MessageTooLargeException, MismatchedDevicesException {
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
 
       final byte deviceId = Device.PRIMARY_ID;
       final int registrationId = 7;
@@ -244,7 +245,8 @@ class MessagesAnonymousGrpcServiceTest extends
               .setType(SendMessageType.DOUBLE_RATCHET)
               .setPayload(ByteString.copyFrom(payload))
               .build());
-      final byte[] reportSpamToken = TestRandomUtil.nextBytes(64);
+
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(Status.INVALID_ARGUMENT,
           () -> unauthenticatedServiceStub().sendSingleRecipientMessage(
               generateRequest(serviceIdentifier, false, true, messages, UNIDENTIFIED_ACCESS_KEY, null)));
@@ -254,8 +256,7 @@ class MessagesAnonymousGrpcServiceTest extends
     @CartesianTest
     void sendUnrestrictedAccessMessage(
         @CartesianTest.Values(booleans = {true, false}) final boolean useUak,
-        @CartesianTest.Values(booleans = {true, false}) final boolean isUua)
-        throws MessageTooLargeException, MismatchedDevicesException {
+        @CartesianTest.Values(booleans = {true, false}) final boolean isUua) {
 
       final byte deviceId = Device.PRIMARY_ID;
       final int registrationId = 7;
@@ -289,7 +290,8 @@ class MessagesAnonymousGrpcServiceTest extends
     }
 
     @Test
-    void mismatchedDevices() throws MessageTooLargeException, MismatchedDevicesException {
+    void mismatchedDevices()
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte missingDeviceId = Device.PRIMARY_ID;
       final byte extraDeviceId = missingDeviceId + 1;
       final byte staleDeviceId = extraDeviceId + 1;
@@ -328,7 +330,8 @@ class MessagesAnonymousGrpcServiceTest extends
 
     @ParameterizedTest
     @ValueSource(booleans = {true, false})
-    void badCredentials(final boolean useUak) throws MessageTooLargeException, MismatchedDevicesException {
+    void badCredentials(final boolean useUak)
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte deviceId = Device.PRIMARY_ID;
       final int registrationId = 7;
 
@@ -367,7 +370,8 @@ class MessagesAnonymousGrpcServiceTest extends
     }
 
     @Test
-    void destinationNotFound() throws MessageTooLargeException, MismatchedDevicesException {
+    void destinationNotFound()
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
       final AciServiceIdentifier serviceIdentifier = new AciServiceIdentifier(UUID.randomUUID());
 
       final Map<Byte, IndividualRecipientMessageBundle.Message> messages =
@@ -388,7 +392,7 @@ class MessagesAnonymousGrpcServiceTest extends
     }
 
     @Test
-    void pniIdentifierWithUak() throws MessageTooLargeException, MismatchedDevicesException {
+    void pniIdentifierWithUak() {
       final byte deviceId = Device.PRIMARY_ID;
       final int registrationId = 7;
       final Device destinationDevice = DevicesHelper.createDevice(deviceId, CLOCK.millis(), registrationId);
@@ -410,13 +414,15 @@ class MessagesAnonymousGrpcServiceTest extends
       final SendSealedSenderMessageRequest request =
           generateRequest(pniIdentifier, false, true, messages, UNIDENTIFIED_ACCESS_KEY, null);
 
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(
           Status.INVALID_ARGUMENT,
           () -> unauthenticatedServiceStub().sendSingleRecipientMessage(request));
     }
 
     @Test
-    void rateLimited() throws RateLimitExceededException, MessageTooLargeException, MismatchedDevicesException {
+    void rateLimited()
+        throws RateLimitExceededException, MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte deviceId = Device.PRIMARY_ID;
       final int registrationId = 7;
 
@@ -450,7 +456,8 @@ class MessagesAnonymousGrpcServiceTest extends
     }
 
     @Test
-    void oversizedMessage() throws MessageTooLargeException, MismatchedDevicesException {
+    void oversizedMessage()
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte missingDeviceId = Device.PRIMARY_ID;
       final byte extraDeviceId = missingDeviceId + 1;
       final byte staleDeviceId = extraDeviceId + 1;
@@ -470,14 +477,15 @@ class MessagesAnonymousGrpcServiceTest extends
       doThrow(new MessageTooLargeException())
           .when(messageSender).sendMessages(any(), any(), any(), any(), any(), any());
 
-      //noinspection ResultOfMethodCallIgnored
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(Status.INVALID_ARGUMENT,
           () -> unauthenticatedServiceStub().sendSingleRecipientMessage(
               generateRequest(serviceIdentifier, false, true, messages, UNIDENTIFIED_ACCESS_KEY, null)));
     }
 
     @Test
-    void spamWithStatus() throws MessageTooLargeException, MismatchedDevicesException {
+    void spamWithStatus()
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte deviceId = Device.PRIMARY_ID;
       final int registrationId = 7;
 
@@ -502,7 +510,7 @@ class MessagesAnonymousGrpcServiceTest extends
               Optional.of(GrpcChallengeResponse.withStatusException(GrpcExceptions.rateLimitExceeded(null))),
               Optional.empty()));
 
-      //noinspection ResultOfMethodCallIgnored
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(Status.RESOURCE_EXHAUSTED,
           () -> unauthenticatedServiceStub().sendSingleRecipientMessage(
               generateRequest(serviceIdentifier, false, true, messages, UNIDENTIFIED_ACCESS_KEY, null)));
@@ -516,7 +524,8 @@ class MessagesAnonymousGrpcServiceTest extends
     }
 
     @Test
-    void spamWithResponse() throws MessageTooLargeException, MismatchedDevicesException {
+    void spamWithResponse()
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte deviceId = Device.PRIMARY_ID;
       final int registrationId = 7;
 
@@ -544,6 +553,8 @@ class MessagesAnonymousGrpcServiceTest extends
 
       final SendSealedSenderMessageRequest request =
           generateRequest(serviceIdentifier, false, true, messages, UNIDENTIFIED_ACCESS_KEY, null);
+
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(Status.RESOURCE_EXHAUSTED, () ->
           unauthenticatedServiceStub().sendSingleRecipientMessage(request));
 
@@ -555,6 +566,42 @@ class MessagesAnonymousGrpcServiceTest extends
       verify(messageSender, never()).sendMessages(any(), any(), any(), any(), any(), any());
     }
 
+    @Test
+    void messageDeliveryNotAllowed()
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
+      final byte deviceId = Device.PRIMARY_ID;
+      final int registrationId = 7;
+
+      final Device destinationDevice = DevicesHelper.createDevice(deviceId, CLOCK.millis(), registrationId);
+
+      final Account destinationAccount = mock(Account.class);
+      when(destinationAccount.getDevices()).thenReturn(List.of(destinationDevice));
+      when(destinationAccount.getDevice(deviceId)).thenReturn(Optional.of(destinationDevice));
+      when(destinationAccount.getUnidentifiedAccessKey()).thenReturn(Optional.of(UNIDENTIFIED_ACCESS_KEY));
+
+      final AciServiceIdentifier serviceIdentifier = new AciServiceIdentifier(UUID.randomUUID());
+      when(accountsManager.getByServiceIdentifier(serviceIdentifier)).thenReturn(Optional.of(destinationAccount));
+
+      final byte[] payload = TestRandomUtil.nextBytes(128);
+
+      final Map<Byte, IndividualRecipientMessageBundle.Message> messages =
+          Map.of(deviceId, IndividualRecipientMessageBundle.Message.newBuilder()
+              .setRegistrationId(registrationId)
+              .setPayload(ByteString.copyFrom(payload))
+              .setType(SendMessageType.UNIDENTIFIED_SENDER)
+              .build());
+
+      doThrow(MessageDeliveryNotAllowedException.class)
+          .when(messageSender).sendMessages(any(), any(), any(), any(), any(), any());
+
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
+      GrpcTestUtils.assertStatusException(Status.UNAVAILABLE,
+          () -> unauthenticatedServiceStub().sendSingleRecipientMessage(
+              generateRequest(serviceIdentifier, false, false, messages,
+                  null,
+                  GROUP_SEND_TOKEN)));
+    }
+
     private static SendSealedSenderMessageRequest generateRequest(final ServiceIdentifier serviceIdentifier,
         final boolean ephemeral,
         final boolean urgent,
@@ -595,7 +642,7 @@ class MessagesAnonymousGrpcServiceTest extends
     @CartesianTest
     void sendMessage(@CartesianTest.Values(booleans = {true, false}) final boolean ephemeral,
         @CartesianTest.Values(booleans = {true, false}) final boolean urgent)
-        throws MessageTooLargeException, MultiRecipientMismatchedDevicesException {
+        throws MessageTooLargeException, MultiRecipientMismatchedDevicesException, MessageDeliveryNotAllowedException {
 
       final byte deviceId = Device.PRIMARY_ID;
       final int registrationId = 7;
@@ -656,7 +703,8 @@ class MessagesAnonymousGrpcServiceTest extends
     }
 
     @Test
-    void mismatchedDevices() throws MessageTooLargeException, MultiRecipientMismatchedDevicesException {
+    void mismatchedDevices()
+        throws MessageTooLargeException, MultiRecipientMismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte missingDeviceId = Device.PRIMARY_ID;
       final byte extraDeviceId = missingDeviceId + 1;
       final byte staleDeviceId = extraDeviceId + 1;
@@ -704,7 +752,8 @@ class MessagesAnonymousGrpcServiceTest extends
     }
 
     @Test
-    void badCredentials() throws MessageTooLargeException, MultiRecipientMismatchedDevicesException {
+    void badCredentials()
+        throws MessageTooLargeException, MultiRecipientMismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte deviceId = Device.PRIMARY_ID;
       final int registrationId = 7;
 
@@ -739,7 +788,7 @@ class MessagesAnonymousGrpcServiceTest extends
               .setUrgent(true)
               .build()));
 
-      //noinspection ResultOfMethodCallIgnored
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(Status.INVALID_ARGUMENT, () ->
           unauthenticatedServiceStub().sendMultiRecipientMessage(SendMultiRecipientMessageRequest.newBuilder()
               .setMessage(MultiRecipientMessage.newBuilder()
@@ -755,8 +804,9 @@ class MessagesAnonymousGrpcServiceTest extends
     }
 
     @Test
-    void badPayload() throws MessageTooLargeException, MultiRecipientMismatchedDevicesException {
-      //noinspection ResultOfMethodCallIgnored
+    void badPayload()
+        throws MessageTooLargeException, MultiRecipientMismatchedDevicesException, MessageDeliveryNotAllowedException {
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(Status.INVALID_ARGUMENT, () ->
           unauthenticatedServiceStub().sendMultiRecipientMessage(SendMultiRecipientMessageRequest.newBuilder()
               .setMessage(MultiRecipientMessage.newBuilder()
@@ -765,7 +815,7 @@ class MessagesAnonymousGrpcServiceTest extends
                   .build())
               .build()));
 
-      //noinspection ResultOfMethodCallIgnored
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(Status.INVALID_ARGUMENT, () ->
           unauthenticatedServiceStub().sendMultiRecipientMessage(SendMultiRecipientMessageRequest.newBuilder().build()));
 
@@ -774,7 +824,8 @@ class MessagesAnonymousGrpcServiceTest extends
     }
 
     @Test
-    void repeatedRecipient() throws MessageTooLargeException, MultiRecipientMismatchedDevicesException {
+    void repeatedRecipient()
+        throws MessageTooLargeException, MultiRecipientMismatchedDevicesException, MessageDeliveryNotAllowedException {
       final Device destinationDevice = DevicesHelper.createDevice(Device.PRIMARY_ID, CLOCK.millis(), 1);
 
       final Account destinationAccount = mock(Account.class);
@@ -790,7 +841,7 @@ class MessagesAnonymousGrpcServiceTest extends
 
       final byte[] payload = MultiRecipientMessageHelper.generateMultiRecipientMessage(List.of(recipient, recipient));
 
-      //noinspection ResultOfMethodCallIgnored
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(Status.INVALID_ARGUMENT, () ->
           unauthenticatedServiceStub().sendMultiRecipientMessage(SendMultiRecipientMessageRequest.newBuilder()
               .setGroupSendToken(ByteString.copyFrom(GROUP_SEND_TOKEN))
@@ -807,7 +858,8 @@ class MessagesAnonymousGrpcServiceTest extends
     }
 
     @Test
-    void oversizedMessage() throws MessageTooLargeException, MultiRecipientMismatchedDevicesException {
+    void oversizedMessage()
+        throws MessageTooLargeException, MultiRecipientMismatchedDevicesException, MessageDeliveryNotAllowedException {
       final Account destinationAccount = mock(Account.class);
 
       final AciServiceIdentifier serviceIdentifier = new AciServiceIdentifier(UUID.randomUUID());
@@ -831,13 +883,14 @@ class MessagesAnonymousGrpcServiceTest extends
       doThrow(new MessageTooLargeException())
           .when(messageSender).sendMultiRecipientMessage(any(), any(), anyLong(), anyBoolean(), anyBoolean(), anyBoolean(), any());
 
-      //noinspection ResultOfMethodCallIgnored
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(Status.INVALID_ARGUMENT,
           () -> unauthenticatedServiceStub().sendMultiRecipientMessage(request));
     }
 
     @Test
-    void spamWithStatus() throws MessageTooLargeException, MultiRecipientMismatchedDevicesException {
+    void spamWithStatus()
+        throws MessageTooLargeException, MultiRecipientMismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte deviceId = Device.PRIMARY_ID;
       final int registrationId = 7;
 
@@ -872,7 +925,7 @@ class MessagesAnonymousGrpcServiceTest extends
               Optional.of(GrpcChallengeResponse.withStatusException(GrpcExceptions.rateLimitExceeded(null))),
               Optional.empty()));
 
-      //noinspection ResultOfMethodCallIgnored
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(Status.RESOURCE_EXHAUSTED,
           () -> unauthenticatedServiceStub().sendMultiRecipientMessage(request));
 
@@ -883,7 +936,8 @@ class MessagesAnonymousGrpcServiceTest extends
     }
 
     @Test
-    void spamWithResponse() throws MessageTooLargeException, MultiRecipientMismatchedDevicesException {
+    void spamWithResponse()
+        throws MessageTooLargeException, MultiRecipientMismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte deviceId = Device.PRIMARY_ID;
       final int registrationId = 7;
 
@@ -918,7 +972,7 @@ class MessagesAnonymousGrpcServiceTest extends
       when(spamChecker.checkForMultiRecipientSpamGrpc(any()))
           .thenReturn(new SpamCheckResult<>(Optional.of(GrpcChallengeResponse.withResponse(challengeResponse)), Optional.empty()));
 
-      //noinspection ResultOfMethodCallIgnored
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(Status.RESOURCE_EXHAUSTED,
           () -> unauthenticatedServiceStub().sendMultiRecipientMessage(request));
 
@@ -927,6 +981,41 @@ class MessagesAnonymousGrpcServiceTest extends
       verify(messageSender, never())
           .sendMultiRecipientMessage(any(), any(), anyLong(), anyBoolean(), anyBoolean(), anyBoolean(), any());
     }
+
+    @Test
+    void messageDeliveryNotAllowed()
+        throws MessageTooLargeException, MultiRecipientMismatchedDevicesException, MessageDeliveryNotAllowedException {
+      final byte missingDeviceId = Device.PRIMARY_ID;
+      final byte extraDeviceId = missingDeviceId + 1;
+      final byte staleDeviceId = extraDeviceId + 1;
+
+      final Account destinationAccount = mock(Account.class);
+
+      final AciServiceIdentifier serviceIdentifier = new AciServiceIdentifier(UUID.randomUUID());
+
+      when(accountsManager.getByServiceIdentifierAsync(serviceIdentifier))
+          .thenReturn(CompletableFuture.completedFuture(Optional.of(destinationAccount)));
+
+      final byte[] payload = MultiRecipientMessageHelper.generateMultiRecipientMessage(List.of(
+          new TestRecipient(serviceIdentifier, staleDeviceId, 17, new byte[48])));
+
+      final SendMultiRecipientMessageRequest request = SendMultiRecipientMessageRequest.newBuilder()
+          .setGroupSendToken(ByteString.copyFrom(GROUP_SEND_TOKEN))
+          .setMessage(MultiRecipientMessage.newBuilder()
+              .setTimestamp(CLOCK.millis())
+              .setPayload(ByteString.copyFrom(payload))
+              .build())
+          .setEphemeral(false)
+          .setUrgent(true)
+          .build();
+
+      doThrow(MessageDeliveryNotAllowedException.class)
+          .when(messageSender).sendMultiRecipientMessage(any(), any(), anyLong(), anyBoolean(), anyBoolean(), anyBoolean(), any());
+
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
+      GrpcTestUtils.assertStatusException(Status.UNAVAILABLE,
+          () -> unauthenticatedServiceStub().sendMultiRecipientMessage(request));
+    }
   }
 
   @Nested
@@ -935,7 +1024,7 @@ class MessagesAnonymousGrpcServiceTest extends
     @CartesianTest
     void sendStory(@CartesianTest.Values(booleans = {true, false}) final boolean urgent,
         @CartesianTest.Values(booleans = {true, false}) final boolean includeReportSpamToken)
-        throws MessageTooLargeException, MismatchedDevicesException {
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
 
       final byte deviceId = Device.PRIMARY_ID;
       final int registrationId = 7;
@@ -998,7 +1087,8 @@ class MessagesAnonymousGrpcServiceTest extends
     }
 
     @Test
-    void mismatchedDevices() throws MessageTooLargeException, MismatchedDevicesException {
+    void mismatchedDevices()
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte missingDeviceId = Device.PRIMARY_ID;
       final byte extraDeviceId = missingDeviceId + 1;
       final byte staleDeviceId = extraDeviceId + 1;
@@ -1036,7 +1126,8 @@ class MessagesAnonymousGrpcServiceTest extends
     }
 
     @Test
-    void destinationNotFound() throws MessageTooLargeException, MismatchedDevicesException {
+    void destinationNotFound()
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
       final Map<Byte, IndividualRecipientMessageBundle.Message> messages =
           Map.of(Device.PRIMARY_ID, IndividualRecipientMessageBundle.Message.newBuilder()
               .setRegistrationId(7)
@@ -1053,7 +1144,8 @@ class MessagesAnonymousGrpcServiceTest extends
     }
 
     @Test
-    void rateLimited() throws RateLimitExceededException, MessageTooLargeException, MismatchedDevicesException {
+    void rateLimited()
+        throws RateLimitExceededException, MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte deviceId = Device.PRIMARY_ID;
       final int registrationId = 7;
 
@@ -1085,7 +1177,8 @@ class MessagesAnonymousGrpcServiceTest extends
     }
 
     @Test
-    void oversizedMessage() throws MessageTooLargeException, MismatchedDevicesException {
+    void oversizedMessage()
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte missingDeviceId = Device.PRIMARY_ID;
       final byte extraDeviceId = missingDeviceId + 1;
       final byte staleDeviceId = extraDeviceId + 1;
@@ -1105,13 +1198,14 @@ class MessagesAnonymousGrpcServiceTest extends
 
       doThrow(new MessageTooLargeException()).when(messageSender).sendMessages(any(), any(), any(), any(), any(), any());
 
-      //noinspection ResultOfMethodCallIgnored
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusInvalidArgument(
           () -> unauthenticatedServiceStub().sendStory(generateRequest(serviceIdentifier, false, messages)));
     }
 
     @Test
-    void spamWithStatus() throws MessageTooLargeException, MismatchedDevicesException {
+    void spamWithStatus()
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte deviceId = Device.PRIMARY_ID;
       final int registrationId = 7;
 
@@ -1136,7 +1230,7 @@ class MessagesAnonymousGrpcServiceTest extends
               Optional.of(GrpcChallengeResponse.withStatusException(GrpcExceptions.rateLimitExceeded(null))),
               Optional.empty()));
 
-      //noinspection ResultOfMethodCallIgnored
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(Status.RESOURCE_EXHAUSTED,
           () -> unauthenticatedServiceStub().sendStory(generateRequest(serviceIdentifier, true, messages)));
 
@@ -1149,7 +1243,8 @@ class MessagesAnonymousGrpcServiceTest extends
     }
 
     @Test
-    void spamWithResponse() throws MessageTooLargeException, MismatchedDevicesException {
+    void spamWithResponse()
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte deviceId = Device.PRIMARY_ID;
       final int registrationId = 7;
 
@@ -1174,6 +1269,7 @@ class MessagesAnonymousGrpcServiceTest extends
       when(spamChecker.checkForIndividualRecipientSpamGrpc(any(), any(), any(), any()))
           .thenReturn(new SpamCheckResult<>(Optional.of(GrpcChallengeResponse.withResponse(challengeResponse)), Optional.empty()));
 
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(Status.RESOURCE_EXHAUSTED, () ->
           unauthenticatedServiceStub().sendStory(generateRequest(serviceIdentifier, true, messages)));
 
@@ -1185,6 +1281,38 @@ class MessagesAnonymousGrpcServiceTest extends
       verify(messageSender, never()).sendMessages(any(), any(), any(), any(), any(), any());
     }
 
+    @Test
+    void messageDeliveryNotAllowed()
+        throws MessageTooLargeException, MessageDeliveryNotAllowedException, MismatchedDevicesException {
+      final byte deviceId = Device.PRIMARY_ID;
+      final int registrationId = 7;
+
+      final Device destinationDevice = DevicesHelper.createDevice(deviceId, CLOCK.millis(), registrationId);
+
+      final Account destinationAccount = mock(Account.class);
+      when(destinationAccount.getDevices()).thenReturn(List.of(destinationDevice));
+      when(destinationAccount.getDevice(deviceId)).thenReturn(Optional.of(destinationDevice));
+
+      final AciServiceIdentifier serviceIdentifier = new AciServiceIdentifier(UUID.randomUUID());
+      when(accountsManager.getByServiceIdentifier(serviceIdentifier)).thenReturn(Optional.of(destinationAccount));
+
+      final byte[] payload = TestRandomUtil.nextBytes(128);
+
+      final Map<Byte, IndividualRecipientMessageBundle.Message> messages =
+          Map.of(deviceId, IndividualRecipientMessageBundle.Message.newBuilder()
+              .setRegistrationId(registrationId)
+              .setPayload(ByteString.copyFrom(payload))
+              .setType(SendMessageType.UNIDENTIFIED_SENDER)
+              .build());
+
+      doThrow(MessageDeliveryNotAllowedException.class)
+          .when(messageSender).sendMessages(any(), any(), any(), any(), any(), any());
+
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
+      GrpcTestUtils.assertStatusException(Status.UNAVAILABLE,
+          () -> unauthenticatedServiceStub().sendStory(generateRequest(serviceIdentifier, false, messages)));
+    }
+
     private static SendStoryMessageRequest generateRequest(final ServiceIdentifier serviceIdentifier,
         final boolean urgent,
         final Map<Byte, IndividualRecipientMessageBundle.Message> messages) {
@@ -1207,7 +1335,8 @@ class MessagesAnonymousGrpcServiceTest extends
 
     @ParameterizedTest
     @ValueSource(booleans = {true, false})
-    void sendStory(final boolean urgent) throws MessageTooLargeException, MultiRecipientMismatchedDevicesException {
+    void sendStory(final boolean urgent)
+        throws MessageTooLargeException, MultiRecipientMismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte deviceId = Device.PRIMARY_ID;
       final int registrationId = 7;
 
@@ -1260,7 +1389,8 @@ class MessagesAnonymousGrpcServiceTest extends
     }
 
     @Test
-    void mismatchedDevices() throws MessageTooLargeException, MultiRecipientMismatchedDevicesException {
+    void mismatchedDevices()
+        throws MessageTooLargeException, MultiRecipientMismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte missingDeviceId = Device.PRIMARY_ID;
       final byte extraDeviceId = missingDeviceId + 1;
       final byte staleDeviceId = extraDeviceId + 1;
@@ -1306,8 +1436,9 @@ class MessagesAnonymousGrpcServiceTest extends
     }
 
     @Test
-    void badPayload() throws MessageTooLargeException, MultiRecipientMismatchedDevicesException {
-      //noinspection ResultOfMethodCallIgnored
+    void badPayload()
+        throws MessageTooLargeException, MultiRecipientMismatchedDevicesException, MessageDeliveryNotAllowedException {
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(Status.INVALID_ARGUMENT, () ->
           unauthenticatedServiceStub().sendMultiRecipientStory(SendMultiRecipientStoryRequest.newBuilder()
               .setMessage(MultiRecipientMessage.newBuilder()
@@ -1316,7 +1447,7 @@ class MessagesAnonymousGrpcServiceTest extends
                   .build())
               .build()));
 
-      //noinspection ResultOfMethodCallIgnored
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(Status.INVALID_ARGUMENT, () ->
           unauthenticatedServiceStub().sendMultiRecipientMessage(
               SendMultiRecipientMessageRequest.newBuilder().build()));
@@ -1326,7 +1457,8 @@ class MessagesAnonymousGrpcServiceTest extends
     }
 
     @Test
-    void repeatedRecipient() throws MessageTooLargeException, MultiRecipientMismatchedDevicesException {
+    void repeatedRecipient()
+        throws MessageTooLargeException, MultiRecipientMismatchedDevicesException, MessageDeliveryNotAllowedException {
       final Device destinationDevice = DevicesHelper.createDevice(Device.PRIMARY_ID, CLOCK.millis(), 1);
 
       final Account destinationAccount = mock(Account.class);
@@ -1342,7 +1474,7 @@ class MessagesAnonymousGrpcServiceTest extends
 
       final byte[] payload = MultiRecipientMessageHelper.generateMultiRecipientMessage(List.of(recipient, recipient));
 
-      //noinspection ResultOfMethodCallIgnored
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(Status.INVALID_ARGUMENT, () ->
           unauthenticatedServiceStub().sendMultiRecipientStory(SendMultiRecipientStoryRequest.newBuilder()
               .setMessage(MultiRecipientMessage.newBuilder()
@@ -1357,7 +1489,8 @@ class MessagesAnonymousGrpcServiceTest extends
     }
 
     @Test
-    void oversizedMessage() throws MessageTooLargeException, MultiRecipientMismatchedDevicesException {
+    void oversizedMessage()
+        throws MessageTooLargeException, MultiRecipientMismatchedDevicesException, MessageDeliveryNotAllowedException {
       final Account destinationAccount = mock(Account.class);
 
       final AciServiceIdentifier serviceIdentifier = new AciServiceIdentifier(UUID.randomUUID());
@@ -1379,12 +1512,13 @@ class MessagesAnonymousGrpcServiceTest extends
       doThrow(new MessageTooLargeException())
           .when(messageSender).sendMultiRecipientMessage(any(), any(), anyLong(), anyBoolean(), anyBoolean(), anyBoolean(), any());
 
-      //noinspection ResultOfMethodCallIgnored
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusInvalidArgument(() -> unauthenticatedServiceStub().sendMultiRecipientStory(request));
     }
 
     @Test
-    void spamWithStatus() throws MessageTooLargeException, MultiRecipientMismatchedDevicesException {
+    void spamWithStatus()
+        throws MessageTooLargeException, MultiRecipientMismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte deviceId = Device.PRIMARY_ID;
       final int registrationId = 7;
 
@@ -1417,7 +1551,7 @@ class MessagesAnonymousGrpcServiceTest extends
               Optional.of(GrpcChallengeResponse.withStatusException(GrpcExceptions.rateLimitExceeded(null))),
               Optional.empty()));
 
-      //noinspection ResultOfMethodCallIgnored
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(Status.RESOURCE_EXHAUSTED,
           () -> unauthenticatedServiceStub().sendMultiRecipientStory(request));
 
@@ -1428,7 +1562,8 @@ class MessagesAnonymousGrpcServiceTest extends
     }
 
     @Test
-    void spamWithResponse() throws MessageTooLargeException, MultiRecipientMismatchedDevicesException {
+    void spamWithResponse()
+        throws MessageTooLargeException, MultiRecipientMismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte deviceId = Device.PRIMARY_ID;
       final int registrationId = 7;
 
@@ -1461,6 +1596,7 @@ class MessagesAnonymousGrpcServiceTest extends
       when(spamChecker.checkForMultiRecipientSpamGrpc(any()))
           .thenReturn(new SpamCheckResult<>(Optional.of(GrpcChallengeResponse.withResponse(challengeResponse)), Optional.empty()));
 
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(Status.RESOURCE_EXHAUSTED, () ->
           unauthenticatedServiceStub().sendMultiRecipientStory(request));
 
@@ -1469,5 +1605,47 @@ class MessagesAnonymousGrpcServiceTest extends
       verify(messageSender, never())
           .sendMultiRecipientMessage(any(), any(), anyLong(), anyBoolean(), anyBoolean(), anyBoolean(), any());
     }
+
+    @Test
+    void messageDeliveryNotAllowed()
+        throws MessageTooLargeException, MessageDeliveryNotAllowedException, MultiRecipientMismatchedDevicesException {
+      final byte deviceId = Device.PRIMARY_ID;
+      final int registrationId = 7;
+
+      final Device destinationDevice = DevicesHelper.createDevice(deviceId, CLOCK.millis(), registrationId);
+
+      final Account resolvedAccount = mock(Account.class);
+      when(resolvedAccount.getDevices()).thenReturn(List.of(destinationDevice));
+      when(resolvedAccount.getDevice(deviceId)).thenReturn(Optional.of(destinationDevice));
+
+      final AciServiceIdentifier resolvedServiceIdentifier = new AciServiceIdentifier(UUID.randomUUID());
+      final AciServiceIdentifier unresolvedServiceIdentifier = new AciServiceIdentifier(UUID.randomUUID());
+
+      when(accountsManager.getByServiceIdentifierAsync(resolvedServiceIdentifier))
+          .thenReturn(CompletableFuture.completedFuture(Optional.of(resolvedAccount)));
+
+      final TestRecipient resolvedRecipient =
+          new TestRecipient(resolvedServiceIdentifier, deviceId, registrationId, new byte[48]);
+
+      final TestRecipient unresolvedRecipient =
+          new TestRecipient(unresolvedServiceIdentifier, Device.PRIMARY_ID, 1, new byte[48]);
+
+      final byte[] payload = MultiRecipientMessageHelper.generateMultiRecipientMessage(List.of(
+          resolvedRecipient, unresolvedRecipient));
+
+      doThrow(MessageDeliveryNotAllowedException.class)
+          .when(messageSender).sendMultiRecipientMessage(any(), any(), anyLong(), anyBoolean(), anyBoolean(), anyBoolean(), any());
+
+      final SendMultiRecipientStoryRequest request = SendMultiRecipientStoryRequest.newBuilder()
+          .setMessage(MultiRecipientMessage.newBuilder()
+              .setTimestamp(CLOCK.millis())
+              .setPayload(ByteString.copyFrom(payload))
+              .build())
+          .build();
+
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
+      GrpcTestUtils.assertStatusException(Status.UNAVAILABLE,
+          () -> unauthenticatedServiceStub().sendMultiRecipientStory(request));
+    }
   }
 }
diff --git a/service/src/test/java/org/whispersystems/textsecuregcm/grpc/MessagesGrpcServiceTest.java b/service/src/test/java/org/whispersystems/textsecuregcm/grpc/MessagesGrpcServiceTest.java
index 59857a06f..423186542 100644
--- a/service/src/test/java/org/whispersystems/textsecuregcm/grpc/MessagesGrpcServiceTest.java
+++ b/service/src/test/java/org/whispersystems/textsecuregcm/grpc/MessagesGrpcServiceTest.java
@@ -43,6 +43,7 @@ import org.signal.chat.messages.SendAuthenticatedSenderMessageRequest;
 import org.signal.chat.messages.SendMessageAuthenticatedSenderResponse;
 import org.signal.chat.messages.SendSyncMessageRequest;
 import org.whispersystems.textsecuregcm.auth.grpc.AuthenticatedDevice;
+import org.whispersystems.textsecuregcm.controllers.MessageDeliveryNotAllowedException;
 import org.whispersystems.textsecuregcm.controllers.MismatchedDevicesException;
 import org.whispersystems.textsecuregcm.controllers.RateLimitExceededException;
 import org.whispersystems.textsecuregcm.entities.MessageProtos;
@@ -156,7 +157,7 @@ class MessagesGrpcServiceTest extends SimpleBaseGrpcTest<MessagesGrpcService, Me
         @CartesianTest.Values(booleans = {true, false}) final boolean ephemeral,
         @CartesianTest.Values(booleans = {true, false}) final boolean urgent,
         @CartesianTest.Values(booleans = {true, false}) final boolean includeReportSpamToken)
-        throws MessageTooLargeException, MismatchedDevicesException {
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
 
       final byte deviceId = Device.PRIMARY_ID;
       final int registrationId = 7;
@@ -250,6 +251,7 @@ class MessagesGrpcServiceTest extends SimpleBaseGrpcTest<MessagesGrpcService, Me
               .setType(SendMessageType.UNIDENTIFIED_SENDER)
               .build());
 
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(Status.INVALID_ARGUMENT, () -> authenticatedServiceStub()
           .sendMessage(generateRequest(serviceIdentifier, false, true, messages)));
 
@@ -257,7 +259,8 @@ class MessagesGrpcServiceTest extends SimpleBaseGrpcTest<MessagesGrpcService, Me
     }
 
     @Test
-    void mismatchedDevices() throws MessageTooLargeException, MismatchedDevicesException {
+    void mismatchedDevices()
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte missingDeviceId = Device.PRIMARY_ID;
       final byte extraDeviceId = missingDeviceId + 1;
       final byte staleDeviceId = extraDeviceId + 1;
@@ -294,7 +297,8 @@ class MessagesGrpcServiceTest extends SimpleBaseGrpcTest<MessagesGrpcService, Me
     }
 
     @Test
-    void destinationNotFound() throws MessageTooLargeException, MismatchedDevicesException {
+    void destinationNotFound()
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
       final AciServiceIdentifier serviceIdentifier = new AciServiceIdentifier(UUID.randomUUID());
 
       final Map<Byte, IndividualRecipientMessageBundle.Message> messages =
@@ -312,7 +316,8 @@ class MessagesGrpcServiceTest extends SimpleBaseGrpcTest<MessagesGrpcService, Me
     }
 
     @Test
-    void rateLimited() throws RateLimitExceededException, MessageTooLargeException, MismatchedDevicesException {
+    void rateLimited()
+        throws RateLimitExceededException, MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte deviceId = Device.PRIMARY_ID;
       final int registrationId = 7;
 
@@ -347,7 +352,8 @@ class MessagesGrpcServiceTest extends SimpleBaseGrpcTest<MessagesGrpcService, Me
     }
 
     @Test
-    void oversizedMessage() throws MessageTooLargeException, MismatchedDevicesException {
+    void oversizedMessage()
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte missingDeviceId = Device.PRIMARY_ID;
       final byte extraDeviceId = missingDeviceId + 1;
       final byte staleDeviceId = extraDeviceId + 1;
@@ -367,14 +373,15 @@ class MessagesGrpcServiceTest extends SimpleBaseGrpcTest<MessagesGrpcService, Me
       doThrow(new MessageTooLargeException())
           .when(messageSender).sendMessages(any(), any(), any(), any(), any(), any());
 
-      //noinspection ResultOfMethodCallIgnored
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(Status.INVALID_ARGUMENT,
           () -> authenticatedServiceStub().sendMessage(
               generateRequest(serviceIdentifier, false, true, messages)));
     }
 
     @Test
-    void spamWithStatus() throws MessageTooLargeException, MismatchedDevicesException {
+    void spamWithStatus()
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte deviceId = Device.PRIMARY_ID;
       final int registrationId = 7;
 
@@ -399,7 +406,7 @@ class MessagesGrpcServiceTest extends SimpleBaseGrpcTest<MessagesGrpcService, Me
               Optional.of(GrpcChallengeResponse.withStatusException(GrpcExceptions.rateLimitExceeded(null))),
               Optional.empty()));
 
-      //noinspection ResultOfMethodCallIgnored
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(Status.RESOURCE_EXHAUSTED, () -> authenticatedServiceStub()
           .sendMessage(generateRequest(serviceIdentifier, false, true, messages)));
 
@@ -412,7 +419,8 @@ class MessagesGrpcServiceTest extends SimpleBaseGrpcTest<MessagesGrpcService, Me
     }
 
     @Test
-    void spamWithResponse() throws MessageTooLargeException, MismatchedDevicesException {
+    void spamWithResponse()
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte deviceId = Device.PRIMARY_ID;
       final int registrationId = 7;
 
@@ -453,6 +461,38 @@ class MessagesGrpcServiceTest extends SimpleBaseGrpcTest<MessagesGrpcService, Me
       verify(messageSender, never()).sendMessages(any(), any(), any(), any(), any(), any());
     }
 
+    @Test
+    void messageDeliveryNotAllowed()
+        throws MessageTooLargeException, MessageDeliveryNotAllowedException, MismatchedDevicesException {
+      final byte deviceId = Device.PRIMARY_ID;
+      final int registrationId = 7;
+
+      final Device destinationDevice = DevicesHelper.createDevice(deviceId, CLOCK.millis(), registrationId);
+
+      final Account destinationAccount = mock(Account.class);
+      when(destinationAccount.getDevices()).thenReturn(List.of(destinationDevice));
+      when(destinationAccount.getDevice(deviceId)).thenReturn(Optional.of(destinationDevice));
+
+      final AciServiceIdentifier serviceIdentifier = new AciServiceIdentifier(UUID.randomUUID());
+      when(accountsManager.getByServiceIdentifier(serviceIdentifier)).thenReturn(Optional.of(destinationAccount));
+
+      final byte[] payload = TestRandomUtil.nextBytes(128);
+
+      final Map<Byte, IndividualRecipientMessageBundle.Message> messages =
+          Map.of(deviceId, IndividualRecipientMessageBundle.Message.newBuilder()
+              .setRegistrationId(registrationId)
+              .setPayload(ByteString.copyFrom(payload))
+              .setType(SendMessageType.DOUBLE_RATCHET)
+              .build());
+
+      doThrow(MessageDeliveryNotAllowedException.class)
+          .when(messageSender).sendMessages(any(), any(), any(), any(), any(), any());
+
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
+      GrpcTestUtils.assertStatusException(Status.UNAVAILABLE,
+          () -> authenticatedServiceStub().sendMessage(generateRequest(serviceIdentifier, false, false, messages)));
+    }
+
     private static SendAuthenticatedSenderMessageRequest generateRequest(final ServiceIdentifier serviceIdentifier,
         final boolean ephemeral,
         final boolean urgent,
@@ -480,7 +520,7 @@ class MessagesGrpcServiceTest extends SimpleBaseGrpcTest<MessagesGrpcService, Me
     void sendMessage(@CartesianTest.Enum(mode = CartesianTest.Enum.Mode.EXCLUDE, names = {"UNSPECIFIED", "UNRECOGNIZED", "UNIDENTIFIED_SENDER"}) final SendMessageType messageType,
         @CartesianTest.Values(booleans = {true, false}) final boolean urgent,
         @CartesianTest.Values(booleans = {true, false}) final boolean includeReportSpamToken)
-        throws MessageTooLargeException, MismatchedDevicesException {
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
 
       final AciServiceIdentifier serviceIdentifier = new AciServiceIdentifier(AUTHENTICATED_ACI);
       final byte[] payload = TestRandomUtil.nextBytes(128);
@@ -544,7 +584,7 @@ class MessagesGrpcServiceTest extends SimpleBaseGrpcTest<MessagesGrpcService, Me
       ));
 
       if (includeReportSpamToken) {
-        expectedEnvelopes.replaceAll((deviceId, envelope) ->
+        expectedEnvelopes.replaceAll((_, envelope) ->
             envelope.toBuilder().setReportSpamToken(ByteString.copyFrom(reportSpamToken)).build());
       }
 
@@ -563,7 +603,8 @@ class MessagesGrpcServiceTest extends SimpleBaseGrpcTest<MessagesGrpcService, Me
     }
 
     @Test
-    void mismatchedDevices() throws MessageTooLargeException, MismatchedDevicesException {
+    void mismatchedDevices()
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte missingDeviceId = Device.PRIMARY_ID;
       final byte extraDeviceId = missingDeviceId + 1;
       final byte staleDeviceId = extraDeviceId + 1;
@@ -595,7 +636,8 @@ class MessagesGrpcServiceTest extends SimpleBaseGrpcTest<MessagesGrpcService, Me
     }
 
     @Test
-    void rateLimited() throws RateLimitExceededException, MessageTooLargeException, MismatchedDevicesException {
+    void rateLimited()
+        throws RateLimitExceededException, MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
       final Duration retryDuration = Duration.ofHours(7);
       doThrow(new RateLimitExceededException(retryDuration))
           .when(rateLimiter).validate(eq(AUTHENTICATED_ACI), anyLong());
@@ -616,7 +658,8 @@ class MessagesGrpcServiceTest extends SimpleBaseGrpcTest<MessagesGrpcService, Me
     }
 
     @Test
-    void oversizedMessage() throws MessageTooLargeException, MismatchedDevicesException {
+    void oversizedMessage()
+        throws MessageTooLargeException, MismatchedDevicesException, MessageDeliveryNotAllowedException {
       final byte missingDeviceId = Device.PRIMARY_ID;
       final byte extraDeviceId = missingDeviceId + 1;
       final byte staleDeviceId = extraDeviceId + 1;
@@ -636,11 +679,38 @@ class MessagesGrpcServiceTest extends SimpleBaseGrpcTest<MessagesGrpcService, Me
       doThrow(new MessageTooLargeException())
           .when(messageSender).sendMessages(any(), any(), any(), any(), any(), any());
 
-      //noinspection ResultOfMethodCallIgnored
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
       GrpcTestUtils.assertStatusException(Status.INVALID_ARGUMENT, () -> authenticatedServiceStub()
           .sendSyncMessage( generateRequest( true, messages)));
     }
 
+    @Test
+    void messageDeliveryNotAllowed()
+        throws MessageTooLargeException, MessageDeliveryNotAllowedException, MismatchedDevicesException {
+      final AciServiceIdentifier serviceIdentifier = new AciServiceIdentifier(AUTHENTICATED_ACI);
+      final byte[] payload = TestRandomUtil.nextBytes(128);
+
+      final Map<Byte, IndividualRecipientMessageBundle.Message> messages =
+          Map.of(LINKED_DEVICE_ID, IndividualRecipientMessageBundle.Message.newBuilder()
+                  .setRegistrationId(LINKED_DEVICE_REGISTRATION_ID)
+                  .setPayload(ByteString.copyFrom(payload))
+                  .setType(SendMessageType.DOUBLE_RATCHET)
+                  .build(),
+
+              SECOND_LINKED_DEVICE_ID, IndividualRecipientMessageBundle.Message.newBuilder()
+                  .setRegistrationId(SECOND_LINKED_DEVICE_REGISTRATION_ID)
+                  .setPayload(ByteString.copyFrom(payload))
+                  .setType(SendMessageType.DOUBLE_RATCHET)
+                  .build());
+
+      doThrow(MessageDeliveryNotAllowedException.class)
+          .when(messageSender).sendMessages(any(), any(), any(), any(), any(), any());
+
+      //noinspection ResultOfMethodCallIgnored,ThrowableNotThrown
+      GrpcTestUtils.assertStatusException(Status.UNAVAILABLE,
+          () -> authenticatedServiceStub().sendSyncMessage(generateRequest(false, messages)));
+    }
+
     private static SendSyncMessageRequest generateRequest(
         final boolean urgent,
         final Map<Byte, IndividualRecipientMessageBundle.Message> messages) {
diff --git a/service/src/test/java/org/whispersystems/textsecuregcm/push/MessageSenderTest.java b/service/src/test/java/org/whispersystems/textsecuregcm/push/MessageSenderTest.java
index 72d09e052..1ced7f97c 100644
--- a/service/src/test/java/org/whispersystems/textsecuregcm/push/MessageSenderTest.java
+++ b/service/src/test/java/org/whispersystems/textsecuregcm/push/MessageSenderTest.java
@@ -39,6 +39,9 @@ import org.junitpioneer.jupiter.cartesian.CartesianTest;
 import org.signal.libsignal.protocol.InvalidMessageException;
 import org.signal.libsignal.protocol.InvalidVersionException;
 import org.signal.libsignal.protocol.SealedSenderMultiRecipientMessage;
+import org.whispersystems.textsecuregcm.configuration.dynamic.DynamicConfiguration;
+import org.whispersystems.textsecuregcm.configuration.dynamic.DynamicMessageDeliveryConfiguration;
+import org.whispersystems.textsecuregcm.controllers.MessageDeliveryNotAllowedException;
 import org.whispersystems.textsecuregcm.controllers.MismatchedDevices;
 import org.whispersystems.textsecuregcm.controllers.MismatchedDevicesException;
 import org.whispersystems.textsecuregcm.controllers.MultiRecipientMismatchedDevicesException;
@@ -51,6 +54,7 @@ import org.whispersystems.textsecuregcm.metrics.UserAgentTagUtil;
 import org.whispersystems.textsecuregcm.spam.MessageDeliveryListener;
 import org.whispersystems.textsecuregcm.storage.Account;
 import org.whispersystems.textsecuregcm.storage.Device;
+import org.whispersystems.textsecuregcm.storage.DynamicConfigurationManager;
 import org.whispersystems.textsecuregcm.storage.MessagesManager;
 import org.whispersystems.textsecuregcm.tests.util.MultiRecipientMessageHelper;
 import org.whispersystems.textsecuregcm.tests.util.TestRecipient;
@@ -62,6 +66,8 @@ class MessageSenderTest {
   private PushNotificationManager pushNotificationManager;
   private MessageDeliveryListener messageDeliveryListener;
 
+  private DynamicMessageDeliveryConfiguration dynamicMessageDeliveryConfiguration;
+
   private MessageSender messageSender;
 
   @BeforeEach
@@ -70,7 +76,17 @@ class MessageSenderTest {
     pushNotificationManager = mock(PushNotificationManager.class);
     messageDeliveryListener = mock(MessageDeliveryListener.class);
 
-    messageSender = new MessageSender(messagesManager, pushNotificationManager);
+    dynamicMessageDeliveryConfiguration = mock(DynamicMessageDeliveryConfiguration.class);
+
+    final DynamicConfiguration dynamicConfiguration = mock(DynamicConfiguration.class);
+    when(dynamicConfiguration.getMessageDeliveryConfiguration()).thenReturn(dynamicMessageDeliveryConfiguration);
+
+    @SuppressWarnings("unchecked") final DynamicConfigurationManager<DynamicConfiguration> dynamicConfigurationManager =
+        mock(DynamicConfigurationManager.class);
+
+    when(dynamicConfigurationManager.getConfiguration()).thenReturn(dynamicConfiguration);
+
+    messageSender = new MessageSender(messagesManager, pushNotificationManager, dynamicConfigurationManager);
     messageSender.addMessageDeliveryListener(messageDeliveryListener);
   }
 
@@ -182,6 +198,36 @@ class MessageSenderTest {
         anyBoolean());
   }
 
+  @Test
+  void sendMessageReadOnlyMode() {
+    final UUID accountIdentifier = UUID.randomUUID();
+    final ServiceIdentifier serviceIdentifier = new AciServiceIdentifier(accountIdentifier);
+    final byte deviceId = Device.PRIMARY_ID;
+    final int registrationId = 17;
+
+    final Account account = mock(Account.class);
+    final Device device = mock(Device.class);
+    final MessageProtos.Envelope message = MessageProtos.Envelope.newBuilder().build();
+
+    when(account.getUuid()).thenReturn(accountIdentifier);
+    when(account.getIdentifier(IdentityType.ACI)).thenReturn(accountIdentifier);
+    when(account.isIdentifiedBy(serviceIdentifier)).thenReturn(true);
+    when(account.getDevices()).thenReturn(List.of(device));
+    when(account.getDevice(deviceId)).thenReturn(Optional.of(device));
+    when(device.getId()).thenReturn(deviceId);
+    when(device.getRegistrationId(IdentityType.ACI)).thenReturn(registrationId);
+    when(device.getApnId()).thenReturn("apns-token");
+
+    when(dynamicMessageDeliveryConfiguration.isReadOnly()).thenReturn(true);
+
+    assertThrows(MessageDeliveryNotAllowedException.class, () -> messageSender.sendMessages(account,
+        serviceIdentifier,
+        Map.of(device.getId(), message),
+        Map.of(device.getId(), registrationId),
+        Optional.empty(),
+        null));
+  }
+
   @CartesianTest
   void sendMultiRecipientMessage(@CartesianTest.Values(booleans = {true, false}) final boolean clientPresent,
       @CartesianTest.Values(booleans = {true, false}) final boolean ephemeral,
@@ -303,6 +349,48 @@ class MessageSenderTest {
         anyBoolean());
   }
 
+  @Test
+  void sendMultiRecipientMessageReadOnlyMode()
+      throws NotPushRegisteredException, InvalidMessageException, InvalidVersionException {
+
+    final UUID accountIdentifier = UUID.randomUUID();
+    final ServiceIdentifier serviceIdentifier = new AciServiceIdentifier(accountIdentifier);
+    final byte deviceId = Device.PRIMARY_ID;
+    final int registrationId = 17;
+
+    final Account account = mock(Account.class);
+    final Device device = mock(Device.class);
+
+    when(account.getUuid()).thenReturn(accountIdentifier);
+    when(account.getIdentifier(IdentityType.ACI)).thenReturn(accountIdentifier);
+    when(account.isIdentifiedBy(serviceIdentifier)).thenReturn(true);
+    when(account.getDevices()).thenReturn(List.of(device));
+    when(account.getDevice(deviceId)).thenReturn(Optional.of(device));
+    when(device.getId()).thenReturn(deviceId);
+    when(device.getRegistrationId(IdentityType.ACI)).thenReturn(registrationId);
+    when(device.getApnId()).thenReturn("apns-token");
+    when(device.getApnId()).thenReturn("apns-token");
+
+    final SealedSenderMultiRecipientMessage multiRecipientMessage =
+        SealedSenderMultiRecipientMessage.parse(MultiRecipientMessageHelper.generateMultiRecipientMessage(
+            List.of(new TestRecipient(serviceIdentifier, deviceId, registrationId, new byte[48]))));
+
+    final SealedSenderMultiRecipientMessage.Recipient recipient =
+        multiRecipientMessage.getRecipients().values().iterator().next();
+
+    when(dynamicMessageDeliveryConfiguration.isReadOnly()).thenReturn(true);
+
+    assertThrows(MessageDeliveryNotAllowedException.class,
+        () -> messageSender.sendMultiRecipientMessage(multiRecipientMessage,
+                Map.of(recipient, account),
+                System.currentTimeMillis(),
+                false,
+                false,
+                false,
+                null)
+            .join());
+  }
+
   @ParameterizedTest
   @MethodSource
   void validateIndividualMessageBundle(final Account destination,
diff --git a/service/src/test/java/org/whispersystems/textsecuregcm/storage/ChangeNumberManagerTest.java b/service/src/test/java/org/whispersystems/textsecuregcm/storage/ChangeNumberManagerTest.java
index cdc81cc9d..4e70bb09d 100644
--- a/service/src/test/java/org/whispersystems/textsecuregcm/storage/ChangeNumberManagerTest.java
+++ b/service/src/test/java/org/whispersystems/textsecuregcm/storage/ChangeNumberManagerTest.java
@@ -35,6 +35,7 @@ import org.signal.libsignal.protocol.IdentityKey;
 import org.signal.libsignal.protocol.ecc.ECKeyPair;
 import org.whispersystems.textsecuregcm.auth.PhoneVerificationTokenManager;
 import org.whispersystems.textsecuregcm.auth.RegistrationLockVerificationManager;
+import org.whispersystems.textsecuregcm.controllers.MessageDeliveryNotAllowedException;
 import org.whispersystems.textsecuregcm.controllers.MismatchedDevicesException;
 import org.whispersystems.textsecuregcm.controllers.RateLimitExceededException;
 import org.whispersystems.textsecuregcm.entities.ECSignedPreKey;
@@ -284,7 +285,7 @@ public class ChangeNumberManagerTest {
 
   @Test
   void changeNumberRateLimited()
-      throws MismatchedDevicesException, InterruptedException, MessageTooLargeException, RateLimitExceededException {
+      throws MismatchedDevicesException, InterruptedException, MessageTooLargeException, RateLimitExceededException, MessageDeliveryNotAllowedException {
     final String originalNumber = PhoneNumberUtil.getInstance().format(
         PhoneNumberUtil.getInstance().getExampleNumber("DE"), PhoneNumberUtil.PhoneNumberFormat.E164);
 
@@ -332,7 +333,7 @@ public class ChangeNumberManagerTest {
 
   @Test
   void changeNumberRegistrationLockFailed()
-      throws MismatchedDevicesException, InterruptedException, MessageTooLargeException, RateLimitExceededException {
+      throws MismatchedDevicesException, InterruptedException, MessageTooLargeException, RateLimitExceededException, MessageDeliveryNotAllowedException {
     final String originalNumber = PhoneNumberUtil.getInstance().format(
         PhoneNumberUtil.getInstance().getExampleNumber("DE"), PhoneNumberUtil.PhoneNumberFormat.E164);