KevinTheJedi Hi Kevin,
Correct, the same username is used to manage more than one e-mail address. This is because a distribution list is used to receive e-mails, and that distribution list is also used as the address when ticket responses are sent. The tickets@ mailbox is a member of this group, and has Send As permissions.
Can you elaborate that each system e-mail needs unique authentication? We've done it this way for years, on multiple distinct deployments of osTicket. We currently have it working on another deployment, with no issues. And, for the instance in this ticket, is was working for over a year before we suddenly ran into this authentication error.
Open to any suggestions, just trying to make sure I understand everything. Thanks a lot!