Categories Exchange 2013

Mailbox Size Increases when Transitioning to Exchange 2013

If you are transitioning from Exchange 2007/2010 to Exchange 2013, we will see that the reported size of the mailboxes will increase around 30 to 40%! Don’t be alarmed just yet. The actual space used by the mailbox database will not increase by 30% as this only refers to the attribution of space used by each individual mailbox.

Basically, Exchange 2013 now includes in the mailbox size attribute all the properties of items in a mailbox, thus providing a more accurate calculation of space taken by items in a mailbox and, therefore, the whole mailbox itself.

The problem with this is that, during a migration, users might exceed their mailbox quota when their mailbox is moved to Exchange 2013 and be prevented from sending and/or receiving e-mails...

So, in order to prevent this from happening, I suggest increasing everyone’s mailbox quota by 40% prior to their move. You can either do this at the mailbox database level if your users are using the database quotas, or individually on a per-user basis.

For example, if you want to increase by 40% the ProhibitSendQuota value for all users that are not using the database quota defaults, you can use the following cmdlet:

Get-Mailbox -ResultSize Unlimited -Filter {UseDatabaseQuotaDefaults -eq $False} | Where {$_.ProhibitSendQuota -ne "unlimited"} | ForEach {Set-Mailbox $_ -ProhibitSendQuota "$($($_.ProhibitSendQuota).Value.ToMB() * 1.4)MB" -WhatIf}

However, don’t forget to set the IssueWarningQuota or ProhibitSendReceiveQuota if you are using them! Note that this is not the best method as users might end up with a quota of 1523MB for example when the ideal value would be 1500MB...

Nuno Mota

Nuno Mota is an Exchange MVP working as a Microsoft Messaging Specialist for a financial institution. He is passionate about Exchange, Lync, Active Directory, PowerShell, and Security. Besides writing his personal Exchange blog,, he regularly participates in the Exchange TechNet forums and is the author of the book “Microsoft Exchange Server 2013 High Availability.”

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Nuno Mota

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