We have a similar issue but the guy involved is on vacation. In our case it has to do with users who have not configured their account via NPUM and after so many attempts the service stops. We have a School District and the employees have to log in to update their credentials and we had a bunch that never did it so we started removing them from having advanced UM and it started happening less and less. Supposedly Mitel is working on it
From one of their emails
16/Jun/16 08:20:25.983 msb ERROR [26461:4cebb70] masAgent.cpp#3267: Mailbox [17259] with Email-ID[justation@XXXXXX.net] initialized Failed
16/Jun/16 08:20:26.578 msb ERROR [26461:6682b70] masAgent.cpp#3267: Mailbox [17202] with Email-ID[dsoto@XXXXX.net] initialized Failed
Not sure if these users are no longer employed or they simply changed their passcode. Either way, I have removed the existing Advanced UM credentials (UM email address/alias & UM email passcode) from both their mailboxes. If they are still there and wish for UM to work, they will need to re-enter the proper credentials.
Mitel has informed us that they are working on a fix for the issue that you have been experiencing with the UM service failing after too many attempts to connect to mailboxes with bad UM credentials. The fix will be in the next software load expected in the fall. Until then, please continue to let me know each time there is an issue and we will deal with it in the same fashion as above.
Hope it helps
Craig