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Shared Mailboxes on Office 365 and the 5GB Limit

Dec 15, 2012 by Emma Robinson

Office 365 gives you the ability to create shared mailboxes without having to assign a license to them. This means that they are basically free and provide an ideal replacement for Public Folders, allowing multiple users to access a single mailbox that contains a generic email address such as

Unfortunately, many people do not realize that these shared mailboxes are no longer free once they grow over 10GB in size.

Please Note! The maximum size limit for Office 365 Shared Mailboxes used to be 5GB. In September 2013 Microsoft increased this limit to 10GB.

We’ve created a script that will connect to Office 365 and export the mailbox sizes (and size limits) of all the shared mailboxes to a CSV file. You can then use this CSV file to see if any mailboxes are over 10GB in size.

As usual, you can get the script at the Microsoft Script Repository.

Setting quotas on Shared Mailboxes

Ideally, you should set the quota for these mailboxes to 10GB to prevent them from going over this size limit. The easiest way to do this is:

Set-Mailbox shared_mailbox -ProhibitSendReceiveQuota 10GB -ProhibitSendQuota 9.75GB -IssueWarningQuota 9.5GB

You can also set the quota on ALL Shared and Room mailboxes using the following cmdlet

get-mailbox -ResultSize Unlimited -filter {RecipientTypeDetails -eq "SharedMailbox" -or RecipientTypeDetails -eq "RoomMailbox"} | Set-Mailbox -ProhibitSendReceiveQuota 10GB -ProhibitSendQuota 9.75GB -IssueWarningQuota 9.5GB


For more powerful functionality and full utilization of your Office 365 environment, please view our Office 365 management software page to find out more.