Phantom Office 365 Mailboxes

Brass Contributor

Hey everybody - quick overview of what's going on...

 

Hybrid On-Prem with Office 365.  We have mail users (ie: contacts) in the system that do not have mailboxes on-prem or in Office 365.  They have a MSOLUser object in Office 365 but licenses for mailboxes are not assigned.

 

Today I discovered (by accident) that if the user goes to outlook.office.com and logs in with their credentials that OWA will open up and let them into their mailbox. They don't have a mailbox but they have a mailbox.  The users don't have a license, never had a license.  If I then go into powershell and do a get-mailbox they don't exist - I've tried every which way I can to validate they exist.  

 

I can send from the mailboxes without an issue in OWA as well.  The replies are honoring the mail user target address that's associated so no replies are going there.  I'm not able to get Outlook to map to these mailboxes.

 

Is this related to a service feature (teams, groups, etc) that has a requirement for some sort of anchor mailbox?  I'm totally lost on how these should exist.  I really don't want users finding out these are out there and then trying to use them. 

21 Replies

I'm sure I'll find out more from support today but you guys are uncovering what I was suspicious of originally.  It would seem that this is possibly some byproduct of another requirement within the service to have a "mailbox" as an anchor. 

Word from support is "known issue" but they can't give me any timelines or details as to when this will be remedied.  Just something that everybody should be aware of if they're dealing with "mail user" objects.