Our organisation used to be split across 5 sites with 5 separate domains (and physical locations).

We all use the same Office 365 tenancy and domain name (e.g. all of the staff across the 5 sites use firstname.surname@ouremail.com). Each of these domains use AD Sync to sychronise usernames and passwords with our shared Office365 tenancy.

If a user moves from one of these sites to another, how do we move their user account and mailbox in O365?

At the moment, we simply create a new AD account on the domain of the user's new site. We leave the Mail attribute blank and put them in an OU which doesn't synchronise with O365 so their e-mail account remains unchanged. We leave them as active users in the domain of their old site but obviously this causes problems as when the user's password expires after 90 days or they forget their password, we have to contact the user's old site to request a password change.

I'm struggling to clarify the terminology here. Essentially what I'd like to do is move the user from the old site AD to the new site AD and bring their mailbox with them. Is there a way to do this in PowerShell or something along those lines?

The only other thing I can think of doing is:

  1. log the user in to Outlook
  2. save their .PST
  3. delete them from old site AD/sync
  4. create them on new site AD/sync
  5. log them in to new AD-synced e-mail account and import PST

Having to do that for ~20 users is a bit of a faff though. Does anyone have any more efficient options?


I have not validated this yet but I would try:

  1. Migrate user using ADMT.
  2. Disable and move the source account to a non-syncing OU
  3. Sync the source domain, it should remove the user and deactivate mailbox
  4. Make sure the new/target user is active and in a syncing OU.
  5. I believe Azure AD Connect should attempt to match the existing cloud user with the new user, and their unique ID"s should match.

If the above fails, and you get a new user created, you can initatie a restore request from the old mailbox into the new mailbox:

New-MailboxRestoreRequest -SourceMailbox <Mailbox GUID> -TargetMailbox <Mailbox GUID>
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