diff --git a/app/src/main/java/org/thoughtcrime/securesms/messages/MessageDecryptor.kt b/app/src/main/java/org/thoughtcrime/securesms/messages/MessageDecryptor.kt
index 42a1bff159..915d5cb155 100644
--- a/app/src/main/java/org/thoughtcrime/securesms/messages/MessageDecryptor.kt
+++ b/app/src/main/java/org/thoughtcrime/securesms/messages/MessageDecryptor.kt
@@ -133,6 +133,11 @@ object MessageDecryptor {
 
       if (validationResult is EnvelopeContentValidator.Result.Invalid) {
         Log.w(TAG, "${logPrefix(envelope, cipherResult)} Invalid content! ${validationResult.reason}", validationResult.throwable)
+
+        if (FeatureFlags.internalUser()) {
+          postInvalidMessageNotification(context, validationResult.reason)
+        }
+
         return Result.Ignore(envelope, serverDeliveredTimestamp, followUpOperations.toUnmodifiableList())
       }
 
@@ -182,7 +187,7 @@ object MessageDecryptor {
           Log.w(TAG, "${logPrefix(envelope, e)} Decryption error!", e, true)
 
           if (FeatureFlags.internalUser()) {
-            postErrorNotification(context)
+            postDecryptionErrorNotification(context)
           }
 
           if (FeatureFlags.retryReceipts()) {
@@ -324,11 +329,22 @@ object MessageDecryptor {
     }
   }
 
-  private fun postErrorNotification(context: Context) {
+  private fun postDecryptionErrorNotification(context: Context) {
     val notification: Notification = NotificationCompat.Builder(context, NotificationChannels.getInstance().FAILURES)
       .setSmallIcon(R.drawable.ic_notification)
-      .setContentTitle(context.getString(R.string.MessageDecryptionUtil_failed_to_decrypt_message))
-      .setContentText(context.getString(R.string.MessageDecryptionUtil_tap_to_send_a_debug_log))
+      .setContentTitle("[Internal-only] Failed to decrypt a message!")
+      .setContentText("Tap to send a debug log")
+      .setContentIntent(PendingIntent.getActivity(context, 0, Intent(context, SubmitDebugLogActivity::class.java), PendingIntentFlags.mutable()))
+      .build()
+
+    NotificationManagerCompat.from(context).notify(NotificationIds.INTERNAL_ERROR, notification)
+  }
+
+  private fun postInvalidMessageNotification(context: Context, message: String) {
+    val notification: Notification = NotificationCompat.Builder(context, NotificationChannels.getInstance().FAILURES)
+      .setSmallIcon(R.drawable.ic_notification)
+      .setContentTitle("[Internal-only] Received an invalid message!")
+      .setContentText("$message Tap to send a debug log.")
       .setContentIntent(PendingIntent.getActivity(context, 0, Intent(context, SubmitDebugLogActivity::class.java), PendingIntentFlags.mutable()))
       .build()
 
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 43df93a065..b890bc3e38 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -1223,10 +1223,6 @@
     <string name="MediaRepository_all_media">All media</string>
     <string name="MediaRepository__camera">Camera</string>
 
-    <!-- MessageDecryptionUtil -->
-    <string name="MessageDecryptionUtil_failed_to_decrypt_message">Failed to decrypt message</string>
-    <string name="MessageDecryptionUtil_tap_to_send_a_debug_log">Tap to send a debug log</string>
-
     <!-- MessageRecord -->
     <string name="MessageRecord_unknown">Unknown</string>
     <string name="MessageRecord_message_encrypted_with_a_legacy_protocol_version_that_is_no_longer_supported">Received a message encrypted using an old version of Signal that is no longer supported. Please ask the sender to update to the most recent version and resend the message.</string>
diff --git a/libsignal/service/src/main/java/org/whispersystems/signalservice/api/messages/EnvelopeContentValidator.kt b/libsignal/service/src/main/java/org/whispersystems/signalservice/api/messages/EnvelopeContentValidator.kt
index 49641756e3..de3acb60c0 100644
--- a/libsignal/service/src/main/java/org/whispersystems/signalservice/api/messages/EnvelopeContentValidator.kt
+++ b/libsignal/service/src/main/java/org/whispersystems/signalservice/api/messages/EnvelopeContentValidator.kt
@@ -26,6 +26,14 @@ import org.whispersystems.signalservice.internal.push.SignalServiceProtos.Typing
 object EnvelopeContentValidator {
 
   fun validate(envelope: Envelope, content: Content): Result {
+    if (envelope.type == Envelope.Type.PLAINTEXT_CONTENT) {
+      val result: Result? = createPlaintextResultIfInvalid(content)
+
+      if (result != null) {
+        return result
+      }
+    }
+
     return when {
       envelope.story && !content.meetsStoryFlagCriteria() -> Result.Invalid("Envelope was flagged as a story, but it did not have any story-related content!")
       content.hasDataMessage() -> validateDataMessage(envelope, content.dataMessage)
@@ -288,6 +296,47 @@ object EnvelopeContentValidator {
     }
   }
 
+  private fun createPlaintextResultIfInvalid(content: Content): Result? {
+    val errors: MutableList<String> = mutableListOf()
+
+    if (!content.hasDecryptionErrorMessage()) {
+      errors += "Missing DecryptionErrorMessage"
+    }
+    if (content.hasStoryMessage()) {
+      errors += "Unexpected StoryMessage"
+    }
+    if (content.hasSenderKeyDistributionMessage()) {
+      errors += "Unexpected SenderKeyDistributionMessage"
+    }
+    if (content.hasCallMessage()) {
+      errors += "Unexpected CallMessage"
+    }
+    if (content.hasEditMessage()) {
+      errors += "Unexpected EditMessage"
+    }
+    if (content.hasNullMessage()) {
+      errors += "Unexpected NullMessage"
+    }
+    if (content.hasPniSignatureMessage()) {
+      errors += "Unexpected PniSignatureMessage"
+    }
+    if (content.hasReceiptMessage()) {
+      errors += "Unexpected ReceiptMessage"
+    }
+    if (content.hasSyncMessage()) {
+      errors += "Unexpected SyncMessage"
+    }
+    if (content.hasTypingMessage()) {
+      errors += "Unexpected TypingMessage"
+    }
+
+    return if (errors.isNotEmpty()) {
+      Result.Invalid("Invalid PLAINTEXT_CONTENT! Errors: $errors")
+    } else {
+      null
+    }
+  }
+
   private fun validateGroupContextV2(groupContext: GroupContextV2, prefix: String): Result.Invalid? {
     return if (!groupContext.hasMasterKey()) {
       Result.Invalid("$prefix Missing GV2 master key!")