cannot @mention a user in chatter post - [User X] doesn't have access and won't see this update

Question

I cannot @mention a user in chatter post, it shows a message like [User X] doesn't have access and won't see this update. @mention is greyed out when I add that user. This is not happening for all users.

Answer 1

According to documentation, This issue occurs if the person being mentioned does not have access to the record that was just created.

To verify it, You can run a simple SOQL query using UserRecordAccess object:-

SELECT RecordId, HasEditAccess FROM UserRecordAccess WHERE UserId = [single ID] AND RecordId = [single ID]