@TimWalsh I did some more testing with my team and it turns out:
- Super Admins will always have the ability to send emails from any connected inbox, even if they haven’t been given explicit access
- Other users can only send emails from a connected inbox if they have been given explicit access to that inbox
So I would advise to check your user permissions:
- limit the number of Super Admins for security in general
- check access on each connected inbox to ensure only those users who need access to view the inbox + send emails as the inbox have access - remove everyone else (by default I think access is given to everyone which is a bit scary).
Hope this helps.