Can't lookup user by email anymore
Since a while gitlab changed how email addresses of users are exposed or to be more precise not anymore exposed.
This means you can't search for users anymore by email. But also you are not anymore allowed to view the emails of users of a project.
Essentially making it impossible to query gitlab for the user_id based on the receiving email and thus impossible to do auto assignement of tickets based on the from address within the email.
It only works if the users have their email as part of their username.