MAP to Exchange Online Migration Tool

Copper Contributor
 Hello.  I'm looking for anyone with experience with the Exchange Online migration tab
(Admin Centers->Exchange -> Recipients -> Migration)
Are there any guides to using this service anywhere?  I've opened a O365 support ticket, but the basic information the person gets wrong, tells me they know nothing about it.
* I'm coming from an on prem IMAP server  (so I'm only after email here, not calendar,etc..)
* I want to synchronize accounts from on prem IMAP to O365.
* I want the migration tool to keep the accounts synchronized.
   * This includes deleting messages from the O365 account if they have been deleted from the source account (during the subsequent daily update sync's)
Any information shared would be greatly appreciated.
Thank you.
3 Replies

What you're describing would be IMAP synchronization, not necessarily migration. If you're interested in migrating using IMAP, here is a great guide to getting started:

Note that this is meant to onboard users to Office 365 however, not meant for long term synchronization. It will only synchronize one way; from your IMAP source to Exchange Online. If you're interested in bi-directional sync, there are some third party vendors who have solutions for that.


Hope this helps, and please reply if you're looking for more.

Hi Max,

Thank you for clarifying my terminology.. I've got to have the right if I'm going to explain myself correctly. 8-) I've read that page you referenced before.

I am interested in a somewhat long term synchronization.. however my users will not have access to the O365 account until after a final synchronization, so a one way sync will work just fine... as long as it supports deletes. (i.e. initial sync from IMAP to O365 is complete, user deletes messages from IMAP account, incremental sync happens -- the messages that were deleted from the source IMAP are now also deleted on the destination O365).

My use case is 1300 users with a total of about 5TB of email in the on-prem IMAP server (Zimbra).

I've looked at other 3rd party tools, but the O365 ingest rate is just not high enough to consider a weekend cutover event.

And the 3rd party tools I've looked at do not support the deletes referenced above.

If the IMAP sync will actually keep the O365 in sync with the IMAP, then I don't really care if it takes 2 days, 2 weeks, or even a month to get all 1300 users in.

As long as I can do a final sync over a weekend and then switch off my on prem Zimba.


I've been using "Get-MigrationUserStatistics -Identity -IncludeReport | FL" to follow the process, but more insight here would be helpful.

I will take any and all information help you can provide.



IMAP migration will indeed delete items as they are deleted from the source (see item 6):


I get what you're trying to do, and you're on the right track with your powershell commandlets to track the status. With your migration plan though, I would cut over as soon as possible after your mailboxes are synced to avoid errors. The longer you keep them in sync with an IMAP migration, the more likelihood of errors.


Good luck!