Send delivery receipts.

SignalServiceKit/src/Messages/OWSMessageManager.m

@@ -500,9 +500,12 @@ NS_ASSUME_NONNULL_BEGIN
         }
     }
 
-    // Send delivery receipts for "valid data" messages.
+    // Send delivery receipts for "valid data" messages received via UD.
+    BOOL wasReceivedByUD = envelope.type == SSKProtoEnvelopeTypeUnidentifiedSender;
+    if (wasReceivedByUD) {
         [self.deliveryReceiptManager envelopeWasReceived:envelope];
     }
+}
 
 - (void)sendDeliveryReceiptForEnvelope:(SSKProtoEnvelope *)envelope {
     dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),