diff --git a/pkg/connector/backfill.go b/pkg/connector/backfill.go
index 96a6b10..1018697 100644
--- a/pkg/connector/backfill.go
+++ b/pkg/connector/backfill.go
@@ -59,15 +59,21 @@ func (s *SlackClient) FetchMessages(ctx context.Context, params bridgev2.FetchMe
 		return nil, err
 	}
 	convertedMessages := make([]*bridgev2.BackfillMessage, len(chunk.Messages))
+	var maxMsgID string
 	for i, msg := range chunk.Messages {
 		convertedMessages[i] = s.wrapBackfillMessage(ctx, params.Portal, &msg.Msg)
+		if maxMsgID < msg.Timestamp {
+			maxMsgID = msg.Timestamp
+		}
 	}
 	slices.Reverse(convertedMessages)
+	lastRead := s.getLastReadCache(channelID)
 	return &bridgev2.FetchMessagesResponse{
 		Messages: convertedMessages,
 		Cursor:   networkid.PaginationCursor(chunk.ResponseMetadata.Cursor),
 		HasMore:  chunk.HasMore,
 		Forward:  params.Forward,
+		MarkRead: lastRead != "" && maxMsgID != "" && lastRead >= maxMsgID,
 	}, nil
 }
 
diff --git a/pkg/connector/client.go b/pkg/connector/client.go
index 6b75c9d..919f22d 100644
--- a/pkg/connector/client.go
+++ b/pkg/connector/client.go
@@ -72,6 +72,7 @@ func (s *SlackConnector) LoadUserLogin(ctx context.Context, login *bridgev2.User
 			TeamID:    teamID,
 
 			chatInfoCache: make(map[string]chatInfoCacheEntry),
+			lastReadCache: make(map[string]string),
 		}
 	}
 	teamPortalKey := networkid.PortalKey{ID: slackid.MakeTeamPortalID(teamID)}
@@ -101,6 +102,8 @@ type SlackClient struct {
 
 	chatInfoCache     map[string]chatInfoCacheEntry
 	chatInfoCacheLock sync.Mutex
+	lastReadCache     map[string]string
+	lastReadCacheLock sync.Mutex
 }
 
 var _ bridgev2.NetworkAPI = (*SlackClient)(nil)
@@ -157,6 +160,18 @@ func (s *SlackClient) syncTeamPortal(ctx context.Context) error {
 	return nil
 }
 
+func (s *SlackClient) setLastReadCache(channelID, ts string) {
+	s.lastReadCacheLock.Lock()
+	s.lastReadCache[channelID] = ts
+	s.lastReadCacheLock.Unlock()
+}
+
+func (s *SlackClient) getLastReadCache(channelID string) string {
+	s.lastReadCacheLock.Lock()
+	defer s.lastReadCacheLock.Unlock()
+	return s.lastReadCache[channelID]
+}
+
 func (s *SlackClient) SyncChannels(ctx context.Context) {
 	log := zerolog.Ctx(ctx)
 	clientCounts, err := s.Client.ClientCountsContext(ctx, &slack.ClientCountsParams{
@@ -169,15 +184,22 @@ func (s *SlackClient) SyncChannels(ctx context.Context) {
 		return
 	}
 	latestMessageIDs := make(map[string]string, len(clientCounts.Channels)+len(clientCounts.MpIMs)+len(clientCounts.IMs))
+	lastReadCache := make(map[string]string, len(clientCounts.Channels)+len(clientCounts.MpIMs)+len(clientCounts.IMs))
 	for _, ch := range clientCounts.Channels {
 		latestMessageIDs[ch.ID] = ch.Latest
+		lastReadCache[ch.ID] = ch.LastRead
 	}
 	for _, ch := range clientCounts.MpIMs {
 		latestMessageIDs[ch.ID] = ch.Latest
+		lastReadCache[ch.ID] = ch.LastRead
 	}
 	for _, ch := range clientCounts.IMs {
 		latestMessageIDs[ch.ID] = ch.Latest
+		lastReadCache[ch.ID] = ch.LastRead
 	}
+	s.lastReadCacheLock.Lock()
+	s.lastReadCache = lastReadCache
+	s.lastReadCacheLock.Unlock()
 	userPortals, err := s.UserLogin.Bridge.DB.UserPortal.GetAllForLogin(ctx, s.UserLogin.UserLogin)
 	if err != nil {
 		log.Err(err).Msg("Failed to fetch user portals")
diff --git a/pkg/connector/handleslack.go b/pkg/connector/handleslack.go
index 2e8fbf8..26547f4 100644
--- a/pkg/connector/handleslack.go
+++ b/pkg/connector/handleslack.go
@@ -146,12 +146,15 @@ func (s *SlackClient) wrapEvent(ctx context.Context, rawEvt any) (bridgev2.Remot
 
 	case *slack.ChannelMarkedEvent:
 		meta, metaErr = s.makeEventMeta(ctx, evt.Channel, nil, s.UserID, evt.Timestamp)
+		s.setLastReadCache(evt.Channel, evt.Timestamp)
 		wrapped = wrapReadReceipt(&meta)
 	case *slack.IMMarkedEvent:
 		meta, metaErr = s.makeEventMeta(ctx, evt.Channel, nil, s.UserID, evt.Timestamp)
+		s.setLastReadCache(evt.Channel, evt.Timestamp)
 		wrapped = wrapReadReceipt(&meta)
 	case *slack.GroupMarkedEvent:
 		meta, metaErr = s.makeEventMeta(ctx, evt.Channel, nil, s.UserID, evt.Timestamp)
+		s.setLastReadCache(evt.Channel, evt.Timestamp)
 		wrapped = wrapReadReceipt(&meta)
 
 	case *slack.ChannelJoinedEvent: