Moving mailboxes to Exchange Online can feel like a big task, especially when you’re dealing with sync times, batch statuses, and planning the perfect cutover. A question that often arises is: How long does a migration batch actually last in the cloud? Does it run forever? Does it expire quietly in the background? In this article, you will learn how long migration batches stay in Exchange Online.
Migration batches sync phase
When you create a migration batch, it will by default have the option below checked:
Manually completing the batch later (by clicking the “Complete this migration batch” link on the right pane, after the link becomes active.)
When you migrate mailboxes to Exchange Online, the process begins with syncing mailbox data. Exchange copies most of the mailbox content (95 percent) and then pauses the process. After that, it automatically checks every day and syncs any new items. This is known as delta syncing and helps keep everything up to date.
Note: Selecting the Manually completing the batch later will sync the mailboxes up to 95%. After that, every 24 hours, a delta sync will occur. You can then decide when to complete the mailboxes. That is an excellent way to complete the migration batch in the evening or on the weekend.
Even though Exchange Online displays a finish date far in the future, such as December 31, 9999, that is not a real expiration. In reality, these daily syncs continue for about two months from the time the batch was created.
This is what the migration batch statistics look like.
After two months have passed, Exchange Online stops syncing changes automatically. However, if you still need to continue the migration, you can click Resume. This works whether the two months have passed or not.
Migration batch sync phase timeline overview
To help you understand how migration batches work in Exchange Online, here is a simple breakdown of the different phases. The table below shows what happens from the moment a batch starts until it either completes or stops syncing changes.
| Phase | What It Means |
|---|---|
| Initial sync | Most data is copied to the cloud |
| Daily delta sync | Continues for about two months |
| After two months | Syncing stops unless you click Resume |
| Finish date shown | Says year 9999 (ignore that) |
That’s it!
Read more: Get move request batch in Exchange Online »
Conclusion
You learned how long migration batches stay in Exchange Online. That two-month window gives you time to test and confirm that everything works before finishing the migration. When you’re ready, simply complete the batch. If syncing has already stopped, just click Resume to start it again.
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