diff --git a/lib/shared/dm-ops/dm-op-utils.js b/lib/shared/dm-ops/dm-op-utils.js
index 233bccd23..b16f51f70 100644
--- a/lib/shared/dm-ops/dm-op-utils.js
+++ b/lib/shared/dm-ops/dm-op-utils.js
@@ -1,433 +1,491 @@
 // @flow
 
 import invariant from 'invariant';
 import _groupBy from 'lodash/fp/groupBy.js';
 import * as React from 'react';
 import uuid from 'uuid';
 
 import {
   type ProcessDMOperationUtilities,
   type ProcessingPossibilityCheckResult,
 } from './dm-op-spec.js';
 import { dmOpSpecs } from './dm-op-specs.js';
 import { useProcessAndSendDMOperation } from './process-dm-ops.js';
 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,
   DMAddViewerToThreadMembersOperation,
   DMOperation,
   ComposableDMOperation,
 } from '../../types/dm-ops.js';
 import type { RawMessageInfo } from '../../types/message-types.js';
 import type {
   RawThreadInfo,
   ThickRawThreadInfo,
   ThreadInfo,
 } from '../../types/minimally-encoded-thread-permissions-types.js';
 import type { InboundActionMetadata } from '../../types/redux-types.js';
 import {
   outboundP2PMessageStatuses,
   type OutboundP2PMessage,
 } from '../../types/sqlite-types.js';
 import {
   assertThickThreadType,
   thickThreadTypes,
 } from '../../types/thread-types-enum.js';
 import type { LegacyRawThreadInfo } from '../../types/thread-types.js';
 import {
   type DMOperationP2PMessage,
   userActionsP2PMessageTypes,
 } from '../../types/tunnelbroker/user-actions-peer-to-peer-message-types.js';
 import { updateTypes } from '../../types/update-types-enum.js';
 import type { ClientUpdateInfo } from '../../types/update-types.js';
 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(
   message: DMOperation,
   peers: $ReadOnlyArray<{
     +userID: string,
     +deviceID: string,
   }>,
 ): $ReadOnlyArray<OutboundP2PMessage> {
   const opMessage: DMOperationP2PMessage = {
     type: userActionsP2PMessageTypes.DM_OPERATION,
     op: message,
   };
   const plaintext = JSON.stringify(opMessage);
   const outboundP2PMessages = [];
   for (const peer of peers) {
     const messageToPeer: OutboundP2PMessage = {
       messageID: uuid.v4(),
       deviceID: peer.deviceID,
       userID: peer.userID,
       timestamp: new Date().getTime().toString(),
       plaintext,
       ciphertext: '',
       status: outboundP2PMessageStatuses.persisted,
       supportsAutoRetry: dmOpSpecs[message.type].supportsAutoRetry,
     };
     outboundP2PMessages.push(messageToPeer);
   }
   return outboundP2PMessages;
 }
 
 export const dmOperationSpecificationTypes = Object.freeze({
   OUTBOUND: 'OutboundDMOperationSpecification',
   INBOUND: 'InboundDMOperationSpecification',
 });
 
 type OutboundDMOperationSpecificationRecipients =
   | { +type: 'all_peer_devices' | 'self_devices' }
   | { +type: 'some_users', +userIDs: $ReadOnlyArray<string> }
   | { +type: 'all_thread_members', +threadID: string }
   | { +type: 'some_devices', +deviceIDs: $ReadOnlyArray<string> };
 
 // The operation generated on the sending client, causes changes to
 // the state and broadcasting information to peers.
 export type OutboundDMOperationSpecification = {
   +type: 'OutboundDMOperationSpecification',
   +op: DMOperation,
   +recipients: OutboundDMOperationSpecificationRecipients,
   +sendOnly?: boolean,
 };
 
 export type OutboundComposableDMOperationSpecification = {
   +type: 'OutboundDMOperationSpecification',
   +op: ComposableDMOperation,
   +recipients: OutboundDMOperationSpecificationRecipients,
   // Composable DM Ops are created only to be sent, locally we use
   // dedicated mechanism for updating the store.
   +sendOnly: true,
   +composableMessageID: string,
 };
 
 // The operation received from other peers, causes changes to
 // the state and after processing, sends confirmation to the sender.
 export type InboundDMOperationSpecification = {
   +type: 'InboundDMOperationSpecification',
   +op: DMOperation,
   +metadata: ?InboundActionMetadata,
 };
 
 export type DMOperationSpecification =
   | OutboundDMOperationSpecification
   | InboundDMOperationSpecification;
 
 function useCreateMessagesToPeersFromDMOp(): (
   operation: DMOperation,
   recipients: OutboundDMOperationSpecificationRecipients,
 ) => 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 (
       operation: DMOperation,
       recipients: OutboundDMOperationSpecificationRecipients,
     ): Promise<$ReadOnlyArray<OutboundP2PMessage>> => {
       const { viewerID, threadInfos } = utilities;
       if (!viewerID) {
         return [];
       }
 
       let peerUserIDAndDeviceIDs = allPeerUserIDAndDeviceIDs;
       if (recipients.type === 'self_devices') {
         peerUserIDAndDeviceIDs = allPeerUserIDAndDeviceIDs.filter(
           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') {
         const { threadID } = recipients;
         if (!threadInfos[threadID]) {
           console.log(
             `all_thread_members called for threadID ${threadID}, which is ` +
               'missing from the ThreadStore. if sending a message soon after ' +
               'thread creation, consider some_users instead',
           );
         }
         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') {
         const deviceIDs = new Set(recipients.deviceIDs);
         peerUserIDAndDeviceIDs = allPeerUserIDAndDeviceIDs.filter(peer =>
           deviceIDs.has(peer.deviceID),
         );
       }
 
       const thisDeviceID = await getContentSigningKey();
       const targetPeers = peerUserIDAndDeviceIDs.filter(
         peer => peer.deviceID !== thisDeviceID,
       );
       return generateMessagesToPeers(operation, targetPeers);
     },
-    [allPeerUserIDAndDeviceIDs, utilities],
+    [allPeerUserIDAndDeviceIDs, getMissingPeers, utilities],
   );
 }
 
 function getCreateThickRawThreadInfoInputFromThreadInfo(
   threadInfo: ThickRawThreadInfo,
 ): CreateThickRawThreadInfoInput {
   const roleID = Object.keys(threadInfo.roles).pop();
   const thickThreadType = assertThickThreadType(threadInfo.type);
   return {
     threadID: threadInfo.id,
     threadType: thickThreadType,
     creationTime: threadInfo.creationTime,
     parentThreadID: threadInfo.parentThreadID,
     allMemberIDsWithSubscriptions: threadInfo.members.map(
       ({ id, subscription }) => ({
         id,
         subscription,
       }),
     ),
     roleID,
     unread: !!threadInfo.currentUser.unread,
     name: threadInfo.name,
     avatar: threadInfo.avatar,
     description: threadInfo.description,
     color: threadInfo.color,
     containingThreadID: threadInfo.containingThreadID,
     sourceMessageID: threadInfo.sourceMessageID,
     repliesCount: threadInfo.repliesCount,
     pinnedCount: threadInfo.pinnedCount,
     timestamps: threadInfo.timestamps,
   };
 }
 
 function useAddDMThreadMembers(): (
   newMemberIDs: $ReadOnlyArray<string>,
   threadInfo: ThreadInfo,
 ) => Promise<void> {
   const viewerID = useSelector(
     state => state.currentUserInfo && state.currentUserInfo.id,
   );
   const processAndSendDMOperation = useProcessAndSendDMOperation();
   const threadInfos = useSelector(state => state.threadStore.threadInfos);
 
   return React.useCallback(
     async (newMemberIDs: $ReadOnlyArray<string>, threadInfo: ThreadInfo) => {
       const rawThreadInfo = threadInfos[threadInfo.id];
       invariant(rawThreadInfo.thick, 'thread should be thick');
       const existingThreadDetails =
         getCreateThickRawThreadInfoInputFromThreadInfo(rawThreadInfo);
 
       invariant(viewerID, 'viewerID should be set');
       const addViewerToThreadMembersOperation: DMAddViewerToThreadMembersOperation =
         {
           type: 'add_viewer_to_thread_members',
           existingThreadDetails,
           editorID: viewerID,
           time: Date.now(),
           messageID: uuid.v4(),
           addedUserIDs: newMemberIDs,
         };
       const viewerOperationSpecification: OutboundDMOperationSpecification = {
         type: dmOperationSpecificationTypes.OUTBOUND,
         op: addViewerToThreadMembersOperation,
         recipients: {
           type: 'some_users',
           userIDs: newMemberIDs,
         },
         sendOnly: true,
       };
 
       invariant(viewerID, 'viewerID should be set');
       const addMembersOperation: DMAddMembersOperation = {
         type: 'add_members',
         threadID: threadInfo.id,
         editorID: viewerID,
         time: Date.now(),
         messageID: uuid.v4(),
         addedUserIDs: newMemberIDs,
       };
       const newMemberIDsSet = new Set<string>(newMemberIDs);
       const recipientsThreadID =
         threadInfo.type === thickThreadTypes.THICK_SIDEBAR &&
         threadInfo.parentThreadID
           ? threadInfo.parentThreadID
           : threadInfo.id;
 
       const existingMembers =
         threadInfos[recipientsThreadID]?.members
           ?.map(member => member.id)
           ?.filter(memberID => !newMemberIDsSet.has(memberID)) ?? [];
 
       const addMembersOperationSpecification: OutboundDMOperationSpecification =
         {
           type: dmOperationSpecificationTypes.OUTBOUND,
           op: addMembersOperation,
           recipients: {
             type: 'some_users',
             userIDs: existingMembers,
           },
         };
 
       await Promise.all([
         processAndSendDMOperation(viewerOperationSpecification),
         processAndSendDMOperation(addMembersOperationSpecification),
       ]);
     },
     [processAndSendDMOperation, threadInfos, viewerID],
   );
 }
 
 function getThreadUpdatesForNewMessages(
   rawMessageInfos: $ReadOnlyArray<RawMessageInfo>,
   updateInfos: $ReadOnlyArray<ClientUpdateInfo>,
   utilities: ProcessDMOperationUtilities,
 ): Array<ClientUpdateInfo> {
   const { threadInfos, viewerID } = utilities;
 
   const { rawMessageInfos: allNewMessageInfos } = mergeUpdatesWithMessageInfos(
     rawMessageInfos,
     updateInfos,
   );
   const messagesByThreadID = _groupBy(message => message.threadID)(
     allNewMessageInfos,
   );
 
   const updatedThreadInfosByThreadID: {
     [string]: RawThreadInfo | LegacyRawThreadInfo,
   } = {};
   for (const threadID in messagesByThreadID) {
     updatedThreadInfosByThreadID[threadID] = threadInfos[threadID];
   }
   for (const update of updateInfos) {
     const updatedThreadInfo = updateSpecs[update.type].getUpdatedThreadInfo?.(
       update,
       updatedThreadInfosByThreadID,
     );
     if (updatedThreadInfo) {
       updatedThreadInfosByThreadID[updatedThreadInfo.id] = updatedThreadInfo;
     }
   }
 
   const newUpdateInfos: Array<ClientUpdateInfo> = [];
   for (const threadID in messagesByThreadID) {
     const repliesCountIncreasingMessages = messagesByThreadID[threadID].filter(
       message => messageSpecs[message.type].includedInRepliesCount,
     );
 
     let threadInfo = updatedThreadInfosByThreadID[threadID];
 
     if (repliesCountIncreasingMessages.length > 0) {
       const repliesCountIncreaseTime = Math.max(
         repliesCountIncreasingMessages.map(message => message.time),
       );
       const newThreadInfo = {
         ...threadInfo,
         repliesCount:
           threadInfo.repliesCount + repliesCountIncreasingMessages.length,
       };
       newUpdateInfos.push({
         type: updateTypes.UPDATE_THREAD,
         id: uuid.v4(),
         time: repliesCountIncreaseTime,
         threadInfo: newThreadInfo,
       });
       threadInfo = newThreadInfo;
     }
 
     const messagesFromOtherPeers = messagesByThreadID[threadID].filter(
       message => message.creatorID !== viewerID,
     );
     if (messagesFromOtherPeers.length === 0) {
       continue;
     }
     // We take the most recent timestamp to make sure that
     // change_thread_read_status operation older
     // than it won't flip the status to read.
     const time = Math.max(messagesFromOtherPeers.map(message => message.time));
     invariant(threadInfo.thick, 'Thread should be thick');
 
     // We aren't checking if the unread timestamp is lower than the time.
     // We're doing this because we want to flip the thread to unread after
     // any new message from a non-viewer.
     newUpdateInfos.push({
       type: updateTypes.UPDATE_THREAD_READ_STATUS,
       id: uuid.v4(),
       time,
       threadID: threadInfo.id,
       unread: true,
     });
   }
 
   return newUpdateInfos;
 }
 
 async function checkMessageIDConflict(
   dmOperation: DMOperation,
   utilities: ProcessDMOperationUtilities,
 ): Promise<ProcessingPossibilityCheckResult> {
   if (!dmOperation.messageID) {
     return {
       isProcessingPossible: true,
     };
   }
   const messageID = dmOperation.messageID;
   const message = await utilities.fetchMessage(messageID);
   if (message) {
     console.log(
       `Discarded a ${dmOperation.type} operation because ` +
         `message with the same ID ${messageID} already exists ` +
         'in the store',
     );
     return {
       isProcessingPossible: false,
       reason: {
         type: 'invalid',
       },
     };
   }
   return {
     isProcessingPossible: true,
   };
 }
 
 function useSendDMOperationUtils(): $ReadOnly<{
   ...ProcessDMOperationUtilities,
   viewerID: ?string,
 }> {
   const fetchMessage = useGetLatestMessageEdit();
   const threadInfos = useSelector(state => state.threadStore.threadInfos);
   const entryInfos = useSelector(state => state.entryStore.entryInfos);
   const findUserIdentities = useFindUserIdentities();
   const loggedInUserInfo = useLoggedInUserInfo();
   const viewerID = loggedInUserInfo?.id;
   return React.useMemo(
     () => ({
       viewerID,
       fetchMessage,
       threadInfos,
       entryInfos,
       findUserIdentities,
     }),
     [viewerID, fetchMessage, threadInfos, entryInfos, findUserIdentities],
   );
 }
 
 export {
   useCreateMessagesToPeersFromDMOp,
   useAddDMThreadMembers,
   getCreateThickRawThreadInfoInputFromThreadInfo,
   getThreadUpdatesForNewMessages,
   checkMessageIDConflict,
   useSendDMOperationUtils,
 };