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Robert Berger

How to migrate skipped largeitem messages during migration from Exchange 2010 to Office365

I am migrating from Exchange 2010 on SBS 2011 to Exchange Online Plan 1 (Office365) using the cutover migration method.  The migration completes, but there are a large number of messages that were skipped due to them being too large.

1. Can I disable the message size limit and run the migration again?  If yes: (a) Is there a global message size limit that I can disable, or do I need to disable it for each mailbox individually, and (b) to run the migration again, do I just repeat the steps to run the original migration?

2. If I run the migration again, I would want to run it during off hours.  I disabled port 25 on the firewall protecting the on premise Exchange server during the migration.  Can I enable port 25 and allow users to continue to use email today while I wait for another time window to run the migration?  If yes, will emails that they delete and/or move to folders today also be reflected in Office365 after the next migration completes?

asked01/15/2020 10:36
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Last Activity 01/15/2020 11:22

1 Answer(s)

  • Mariette Knap

    Robert,

    In order to change max item sizes you need to connect to Connect to Exchange Online PowerShell | Microsoft Docs. Once that is done you can view max item sizes with

    Get-Mailbox testuser | fl mailboxplan,maxsendsize,maxreceivesize

    This will set your O365 environment but it does not change existing user mailboxes

    Get-MailboxPlan | Set-MailboxPlan -MaxSendSize 150MB -MaxReceiveSize 150MB

    To change limits for all users

    Get-Mailbox | Set-Mailbox -MaxReceiveSize 150MB -MaxSendSize 150MB

    Once a cutover migration has been completed and it did not fail you cannot run it again because it will duplicate everything

    In the case you have now I would complete the cutover migration so that users will use O365 from now on but do not uninstall Exchange Server 2010 yet from the SBS as we can try to export mail to pst files, see Export mailboxes from Exchange Server 2010 to pst files. Exporting may help you to retain the emails that were not migrated but exporting to pst files also has limitations, read Mailbox imports and exports in Exchange Server | Microsoft Docs

    answered 01/15/2020 10:53
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    Robert Berger

    Can I delete all the accounts in O365, remove the size limits for any users, and then run the migration again in order to avoid duplicating the emails, while getting the large items to migrate over during the next attempt?
     

    Mariette Knap

    Hello Robert,

    That may work but I have never done this but I do not see why it would not work. Make sure you 'unlicense' the accounts before you delete them.

    replied 01/15/2020 11:22
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    replied 01/15/2020 11:05
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