How to convert Legacy Mailboxes to regular User Mailboxes after Exchange upgrade
If you recently completed a transition from Exchange 2003/2007 to 2010 you probably noticed that some of the migrated mailboxes are marked as Legacy Mailboxes.
In order to change all Legacy mailbox to regular mailboxes, you can run the following PowerShell cmdlet: :
Get-Mailbox -ResultSize unlimited -Filter {RecipientTypeDetails -eq “LegacyMailbox”} | Set-Mailbox –ApplyMandatoryProperties
In order to convert specific mailboxes to regular mailboxes, run the following PowerShell cmdlet:
Set-Mailbox -Identity -ApplyMandatoryProperties

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