How do I migrate large mail items to Office 365?




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    Jason Wagner

    You can change the default for an organization by adjusting the default message size restriction. In the Exchange admin center Simply select recipients mailboxes then click “. . .” and select Set default message size restrictions.

    Office 365 now supports larger email messages 1 v2
    You can then specify the maximum message size for new mailboxes (only for those you create in the future).

    For existing users...

    To edit multiple mailboxes select recipients > mailboxes and select multiple mailboxes. Then from the Bulk Edit pane under Message Size Restrictions select Update.

    Office 365 now supports larger email messages 3 v2

    You can customize a single mailbox by selecting recipients > mailboxes and then select a user’s mailbox. Click the edit icon , then under Message Size Restrictions, click View details and then specify the maximum message size.

    Credit due to:

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    Georgiy Frolov

    After following the guide - "Connect to Office 365 PowerShell" from Microsoft listed in this KB article, you need to follow additional guide - "Connect to Exchange Online PowerShell"  to be able to execute those PS commands, otherwise you will get errors from PowerShell such as "The term 'Get-Mailbox' is not recognized as the name of a cmdlet, function, script file, or operable". 


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    Mark Keller

    Life saver Georgiy Frolov !

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    Upward Technology

    Gregoriy FTW.

    Thank you.

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    Eden Freeman

    MaxSendSize: 150 MB (36,700,160 bytes)
    MaxReceiveSize: 150 MB (37,748,736 bytes)

    Those numbers don't match up.


    Also, it seems like this does not modify existing mailboxes, only new ones created with that plan/policy.

    Modifying the settings in a mailbox plan doesn't affect existing mailboxes that were created using the mailbox plan. The only way to use a mailbox plan to modify the settings on an existing mailbox is to assign a different license to the user, which will apply the corresponding mailbox plan to the mailbox.


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    Kyle Rinner

    I will have the KB updated so it shows the correct numbers:
    MaxSendSize : 150 MB (157,286,400 bytes)
    MaxReceiveSize : 150 MB (157,286,400 bytes)

    You are correct, the command "Get-MailboxPlan | Set-MailboxPlan -MaxSendSize 150MB -MaxReceiveSize 150MB" does not modify mailboxes that already exist.
    The next command will modify the max size for all existing mailboxes: "Get-Mailbox | Set-Mailbox -MaxReceiveSize 150MB -MaxSendSize 150MB"

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