<!--IssueSummary start--> <details> <summary> Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards. </summary> - [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=17917) </details> <!--IssueSummary end--> ### Description Trigger (slack) mention on chat message (with slack-notifier) The only way to mention a slack user (or group) within attachement is to add slack user ID like that : <@U0272PX3W|user> ### Proposal Add a text field slack user ID Add a checkbox field `on/off` into in [Slack integration setup page] (https://github.com/gitlabhq/gitlabhq/blob/master/doc/user/project/integrations/slack.md) Add somewhere into slack message attachements [Here](https://github.com/gitlabhq/gitlabhq/tree/master/app/models/project_services/chat_message) ### Links / references [Slack message Attachements](https://api.slack.com/docs/message-attachments) [Slack message Formatting](https://api.slack.com/docs/message-formatting) [Sack user ID API](https://api.slack.com/methods/users.list)