diff --git a/lib/shared/dm-ops/dm-op-utils.js b/lib/shared/dm-ops/dm-op-utils.js
--- a/lib/shared/dm-ops/dm-op-utils.js
+++ b/lib/shared/dm-ops/dm-op-utils.js
@@ -14,8 +14,10 @@
 import { useFindUserIdentities } from '../../actions/user-actions.js';
 import { useLoggedInUserInfo } from '../../hooks/account-hooks.js';
 import { useGetLatestMessageEdit } from '../../hooks/latest-message-edit.js';
+import { useGetAndUpdateDeviceListsForUsers } from '../../hooks/peer-list-hooks.js';
 import { mergeUpdatesWithMessageInfos } from '../../reducers/message-reducer.js';
 import { getAllPeerUserIDAndDeviceIDs } from '../../selectors/user-selectors.js';
+import { type P2PMessageRecipient } from '../../tunnelbroker/peer-to-peer-context.js';
 import type {
   CreateThickRawThreadInfoInput,
   DMAddMembersOperation,
@@ -48,6 +50,7 @@
 import { getContentSigningKey } from '../../utils/crypto-utils.js';
 import { useSelector } from '../../utils/redux-utils.js';
 import { messageSpecs } from '../messages/message-specs.js';
+import { userSupportsThickThreads } from '../thread-utils.js';
 import { updateSpecs } from '../updates/update-specs.js';
 
 function generateMessagesToPeers(
@@ -127,6 +130,55 @@
 ) => Promise<$ReadOnlyArray<OutboundP2PMessage>> {
   const allPeerUserIDAndDeviceIDs = useSelector(getAllPeerUserIDAndDeviceIDs);
   const utilities = useSendDMOperationUtils();
+  const auxUserInfos = useSelector(state => state.auxUserStore.auxUserInfos);
+  const getAndUpdateDeviceListsForUsers = useGetAndUpdateDeviceListsForUsers();
+
+  const getUsersWithoutDeviceList = React.useCallback(
+    (userIDs: $ReadOnlyArray<string>) => {
+      const missingDeviceListsUserIDs: Array<string> = [];
+      for (const userID of userIDs) {
+        const supportsThickThreads = userSupportsThickThreads(
+          userID,
+          auxUserInfos,
+        );
+        if (!supportsThickThreads) {
+          missingDeviceListsUserIDs.push(userID);
+        }
+      }
+      return missingDeviceListsUserIDs;
+    },
+    [auxUserInfos],
+  );
+
+  const getMissingPeers = React.useCallback(
+    async (
+      userIDs: $ReadOnlyArray<string>,
+    ): Promise<$ReadOnlyArray<P2PMessageRecipient>> => {
+      const missingDeviceListsUserIDs = getUsersWithoutDeviceList(userIDs);
+      if (missingDeviceListsUserIDs.length === 0) {
+        return [];
+      }
+
+      const deviceLists = await getAndUpdateDeviceListsForUsers(
+        missingDeviceListsUserIDs,
+        true,
+      );
+
+      const updatedPeers: Array<P2PMessageRecipient> = [];
+      for (const userID of missingDeviceListsUserIDs) {
+        if (deviceLists[userID] && deviceLists[userID].devices.length > 0) {
+          updatedPeers.push(
+            ...deviceLists[userID].devices.map(deviceID => ({
+              deviceID,
+              userID,
+            })),
+          );
+        }
+      }
+      return updatedPeers;
+    },
+    [getAndUpdateDeviceListsForUsers, getUsersWithoutDeviceList],
+  );
 
   return React.useCallback(
     async (
@@ -144,8 +196,11 @@
           peer => peer.userID === viewerID,
         );
       } else if (recipients.type === 'some_users') {
+        const missingPeers = await getMissingPeers(recipients.userIDs);
+        const updatedPeers = [...allPeerUserIDAndDeviceIDs, ...missingPeers];
+
         const userIDs = new Set(recipients.userIDs);
-        peerUserIDAndDeviceIDs = allPeerUserIDAndDeviceIDs.filter(peer =>
+        peerUserIDAndDeviceIDs = updatedPeers.filter(peer =>
           userIDs.has(peer.userID),
         );
       } else if (recipients.type === 'all_thread_members') {
@@ -160,8 +215,11 @@
         const members = threadInfos[recipients.threadID]?.members ?? [];
         const memberIDs = members.map(member => member.id);
 
+        const missingPeers = await getMissingPeers(memberIDs);
+        const updatedPeers = [...allPeerUserIDAndDeviceIDs, ...missingPeers];
+
         const userIDs = new Set(memberIDs);
-        peerUserIDAndDeviceIDs = allPeerUserIDAndDeviceIDs.filter(peer =>
+        peerUserIDAndDeviceIDs = updatedPeers.filter(peer =>
           userIDs.has(peer.userID),
         );
       } else if (recipients.type === 'some_devices') {
@@ -177,7 +235,7 @@
       );
       return generateMessagesToPeers(operation, targetPeers);
     },
-    [allPeerUserIDAndDeviceIDs, utilities],
+    [allPeerUserIDAndDeviceIDs, getMissingPeers, utilities],
   );
 }