Help migration from IMAP to Exchange Online.

Alexander LT 0 Reputation points
2023-07-24T07:33:12.5966667+00:00

Hi there, we've recently decided to migrate all of our mail from an IMAP mail server to Exchange online, but I'm having some issues with the migration. Some of the accounts are just not migrating properly. IE:

I created a migration batch with 2 (Relatively large) and 1 (Small) mailbox, The small one syncs no issue, one of the larger ones took a while but synced in the end, but the largest one (about 10GB) is just refusing to continue syncing, it's stuck at 2GB and not advancing, I left it for a whole day and still nothing, I have no idea what can be the problem, it seems to be random, because in another migration batch I had a very large Mailbox (Around 15GB), it took a while, but it synced all the 15 GB. I have no idea what can be the problem, the solution I have found is Exporting the ots file from the old server in outlook and importing it into the migrated mailbox. That's fine when I have a mall amount of accounts, but it just doesn't work when a domain has a lot of mailboxes, and many of them are just not syncing.

I have already posted this question on answers.microsoft.com, and someone suggested me to run some powershell commands, unfortunately I am not able to run commands because I'm using exchange online and I do not have an azure licence to use the cloud shell...

Image

](https://filestore.community.support.microsoft.com/api/images/1dcaf7a5-87d9-4dc4-ac71-16419cdbeee6?upload=true&fud_access=rhYinQu9k%2fQ7lDpdCsGkl3eusmFMeQelfHau4vFjY8lur4WJxfiEK7M3p4%2bs9FkBPy4gjPk1BpzKedTB0Zjh%2bzCRtDd6jCa%2fyokBDwISGOaLz2NNyurtbpNCCvuSAxDElHG%2fn6DLSEvx6me%2bhAe45HBqG7msHLrMHcwqqfox4xH6BTVJZyX8XQWjsNCEjow5PT5KBAIoxI4%2bFAC1nfdLkm5n2uvM2rK3258tzz1o%2b3qvCGS1YrO8AVU3l5lAZaxMof4PpGVIYBlyN6IF2wBTlcloFdlSscWSO5r3w9XlfGCFBxjA3qCmf0JvOSGTgQF7BDLe5F5QaJW4KFAdHh3KDUPGNroK8k3yO%2fly%2fGxQof4%3d"filestore.community.support.microsoft.com")

But This is how my batch looks like form the admin centre:

Image

As you can see, the first mailbox is stuck on "Syncing" And it's been like that since yesterday. The other mailboxes have synced without issues.

I hope somebody has the answer because I've been trying to get this done for well over a week and I have not been able to get it resolved.

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  1. Kael Yao-MSFT 37,691 Reputation points Microsoft Vendor
    2023-07-25T01:31:37.7833333+00:00

    Hi @Alexander LT

    There is a Microsoft KB with detailed information on troubleshooting IMAP migration in Exchange Online.

    For your reference: Troubleshooting issues with IMAP mailbox migration

    Since you are having trouble with slow migration, please follow the steps starting from My migration is slow (if migration is taking longer than expected) part.


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