Improve UX for notifying users without board access

I am experiencing frustration and miscommunication when notifying or @mentioning users who do not have access to a specific board.

When I notify a user about a status change, they receive an email, but if they click the button in the email, they are met with an 'access denied' message.

I need a clear message or improved UX to indicate when a user I am trying to notify or @mention does not have access to the board, preventing ineffective notifications and confusion.