diff --git a/lib/tunnelbroker/peer-to-peer-context.js b/lib/tunnelbroker/peer-to-peer-context.js
--- a/lib/tunnelbroker/peer-to-peer-context.js
+++ b/lib/tunnelbroker/peer-to-peer-context.js
@@ -55,7 +55,7 @@
     contentPayload: string,
     recipients: $ReadOnlyArray<P2PMessageRecipient>,
     authMetadata: AuthMetadata,
-  ) => Promise<void>,
+  ) => Promise<$ReadOnlyArray<string>>,
 };
 
 const PeerToPeerContext: React.Context<?PeerToPeerContextType> =
@@ -377,7 +377,7 @@
       contentPayload: string,
       recipients: $ReadOnlyArray<P2PMessageRecipient>,
       authMetadata: AuthMetadata,
-    ) => {
+    ): Promise<$ReadOnlyArray<string>> => {
       const { userID: thisUserID, deviceID: thisDeviceID } = authMetadata;
       if (!thisDeviceID || !thisUserID) {
         throw new Error('No auth metadata');
@@ -385,6 +385,8 @@
       const { olmAPI } = getConfig();
       await olmAPI.initializeCryptoAccount();
 
+      const recipientsThatReceivedMessages: Array<P2PMessageRecipient> = [];
+
       // 1. Optimistically attempt to send all messages, and all should
       // succeed, the only exceptions are messages for devices we don't
       // have a session with or some other issues like network connection.
@@ -404,6 +406,9 @@
       const userDevicesWithoutSession: { [userID: string]: Array<string> } = {};
       const recipientsToRetry: Array<P2PMessageRecipient> = [];
       for (const result of messagesResults) {
+        if (result.status === 'success') {
+          recipientsThatReceivedMessages.push(result.recipient);
+        }
         if (result.status === 'missing_session') {
           recipientsToRetry.push(result.recipient);
           const { userID, deviceID } = result.recipient;
@@ -415,7 +420,9 @@
         }
       }
       if (recipientsToRetry.length === 0) {
-        return;
+        return recipientsThatReceivedMessages.map(
+          recipient => recipient.deviceID,
+        );
       }
 
       // 3.Create a session with users which has at
@@ -436,7 +443,15 @@
           olmDebugLog,
         ),
       );
-      await Promise.all(retryPromises);
+      const retryResults = await Promise.all(retryPromises);
+      for (const result of retryResults) {
+        if (result.status === 'success') {
+          recipientsThatReceivedMessages.push(result.recipient);
+        }
+      }
+      return recipientsThatReceivedMessages.map(
+        recipient => recipient.deviceID,
+      );
     },
     [addLog, olmDebugLog, peerOlmSessionsCreator, sendMessageToDevice],
   );