User voicemail fails sort of and Office 365

[agrizzle]

Good morning all, I'm on day 27 of trying to assist our VOIP person with a single user account that is giving issues with Single Inbox messages. Out of all the users we service this single account is throwing an error that I can't figure out. Please see the below image for the error. 

Cisco provided our VOIP person the Microsoft Remote Connectivity Analyzer and the settings to use. When attempting to complete a test with those settings, the tool returns that it can find the account, but it can't create a new item and Error Mailbox Configuration: <nothing>. The weird thing is if I change the test to use user principal name instead of SMTP, it works and something triggers so the user will start getting voicemails. After testing with user principal name and switching back to SMTP the test will run successfully against SMTP instead of failing. This is where I'm at the head scratching part. It'll stay fixed for a little while, 30 minutes maybe an hour or two, then revert back to not working. 

I've checked from my side (365) and the user name and smtp match as they should. I can find her seven ways to Sunday. There are no conflicting accounts. Does anyone have any possible suggestions as to why this account is doing this or what may be triggering the 365 sides connection to work suddenly?

 

[agrizzle]

I'm posting what fixed this issue in case someone runs across it in a few years. This user was created in a new domain that had no permissions or accesses set. It caused so many issues we deleted the user and created a new account on the old domain. I say created, I'm 99% sure the admin for that agency copy and pasted the other account instead of doing a fresh new user. The theory is this left enough attributes and strange bits, that UM was trying to attach to the deleted mailbox. I ended up having to go out and permanently delete the mailbox.