I'm migrating mailbox to Office 365 and got stuck with Large Items Exception.

I read about default message size restrictions. And set 100MB limit in Exchange Online.

Then migration failed again. I checked large item. It is around 40MB. So just above previous size restriction.

Since then I've tried to find any place where 35MB old limit is applied. Either on-premise or in cloud. And the only place I found is Mailuser in cloud. It's Mailuser because mailbox is still on-premise

The command run in Exchange Online. enter image description here

I've confirmed that. After migration large item was skipped. And cloud mailbox MaxSendSize and MaxReceiveSize were 35 and 36 respectfully. Where they should have been 100MB as default message size restriction.

Could you please help? Maybe you know where this numbers are coming from. Or some policy for migration message size. I'd appreciate any thoughts.

Update 12.02.20. It seems to work after disabling data-loss prevention policy. We had Office 365 Security and Compliance DLP scanning Exchange mail. After deleting this, migration works, and message size restriction is back to default setting of 100MB for newly migrated mailbox. Maybe DLP freezes this restriction, I don't know.

  • I read about default message size restrictions. And set 100MB limit in Exchange Online. - What command did you run to set it? Try running Get-Mailbox | Set-Mailbox -MaxReceiveSize 150MB -MaxSendSize 150MB and check it again. – joeqwerty Feb 3 '20 at 11:54

Office 365 Exchange Online message size onboarding limit increase — We are making a change to allow customers to migrate larger mail messages to Exchange Online. We now allow messages up to 150MB to be migrated to the service. We are not changing other limits such as mailbox size or maximum send/receive limit for messages. So you need to change the maximum send/receive limit manually.

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