Exchange Online Migration Batches–How Long Do They Exist For

When you create a migration batch in Exchange Online, the default setting for a migration is to start the batch immediately and complete manually. So how long can you leave this batch before you need to complete it?

As you can see from the below screenshot, the migration batch here was created on Feb 19th, which was only yesterday as I write this blog.


The batch was created on the morning of the 19th Feb, and set to manual start (rather than the default of automatic start, as did not want to migrate lots of data during the business day) and then it was started close to 5:30pm that evening. By 11:25pm the batch had completed its initial sync of all 28 mailboxes and there were no failures. There were other batches syncing at the same time, so this is not indicative of any expected or determined migration performance speeds.

So what happens next. In the background a new mailbox move request was created for each mailbox in the batch, and each individual mailbox was synced to Exchange Online and associated with the synced Mail User object created in the cloud by the AADSync process. When each move reached 95% complete, the move was suspended. It will be resumed around 24 hours later, so that each mailbox is kept up to date once a day automatically.

If you leave the migration running but not completed you will see from the migration batch status above that the batch will complete in 7,981 years (on the 31st Dec 9999 and one second before the next millennium bug hits). In the meantime the migration batch sync will stop doing its daily updates after two months.

After two months of syncing to the cloud and not being completed, Exchange Online assumes you are still no closer to migrating and they stop keeping the mailbox on-premise and the mailbox in the cloud in sync. You can restart this process by interacting with the migration batch before this time, or if it does stop by just clicking the Resume icon, and this will restart it for a further period of time.




7 responses to “Exchange Online Migration Batches–How Long Do They Exist For”

  1. Kiran Ramesh avatar
    Kiran Ramesh

    7981 years . Nice catch

  2. Rkast avatar

    But did you assign a license to the cloud user? Or when a mailbox is synced does it not ‘expire’ or get removed after 30 days if no license is assigned?

    1. Brian Reid avatar

      The users in this case are licenced. But I know that 30 days does not expire the object if there is no licence assigned. It has not been like that for years, contrary to popular opinion. The 30 days with no licence is for a mailbox and not a mail user being migrated.

      1. Rkast avatar

        Ok for hybrid i can imagine thats the case. But what for cutover migration, tegen the user is not a mailuser but a mailbox user.

        1. Brian Reid avatar

          If it’s a mailbox then it needs a license, as you cannot have a mailbox without one. Hybrid results in a mailuser after licensing, and when the move completed a mailbox. If you move an unlinenced mailbox to the cloud you have a 30 day grace period

          1. DavidJ avatar

            So if your in a hybrid environment, you can leave the batches at 95% synced for a maximum of 2 months before completing? I ask because or connector only allows 10 mailboxes to be moved at one time and we were thinking of completing them all on a 3 day weekend.

          2. Brian Reid avatar

            They will stay around longer than 2 months. The auto complete date on a migration batch is “31/12/9999 23:59:59”

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