Office 365 – Migrating Mailboxes from on premise to office 365

Posted by on 10 Feb, 2015 in Microsoft, Office 365 | 0 comments


Hybrid Setup Exchange 2010 and Office 365


When migrating mailboxes in batches to office 365 using the Office 365 admin portal I had a couple of mailboxes fail when the mailbox status was completing. After about 20 minutes with mailboxes being stuck on completing. The following error appeared in the logs:

Error: SyncTimeoutException: Email migration failed for this user because no email could be downloaded


To resolve the issue with the mailboxes I deleted them from the batch and created a separate batch with the failed mailbox(s) and ran the migration again. This resolved the issue. When migrating mailboxes I found that migration them in batched of about 20-25 worked fine. When I had larger numbers or total emails for the batch exceeding 400-450k it seemed to cause issues. It could have just been coincidence but the smaller batches worked fine.

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