Mark messages as unread
Available on all plans
Cloud and self-hosted deployments
If you read a message, but don’t have time to address it right away, you can mark that message as unread. Marking a message as unread displays the channel as bold in the channel sidebar, and groups the message with all other unread messages.
Hover over the message, select the More option, then select Mark as Unread.
Long press a message, and then tap Mark as Unread.