Disabling automatic assignment in Outlook to mailboxes with Full Access permissions

Starting with Exchange 2010 Service Pack 1 (SP1), a feature was introduced that allows Outlook 2007 and Outlook 2010 clients to automatically assign any mailbox to which a user has full access permissions. If a user has full access permissions to another user's mailbox or to a shared mailbox, Outlook automatically loads all mailboxes to which the user has full access.

However, it should be noted that these mailboxes generate space in the data file (ost) of the main mailbox and can cause it to fill up very quickly, in addition to queries being too slow or even Outlook itself taking a long time to load.

If what we need is to have Full Access to a mailbox without affecting Outlook performance, we can remove the automatic assignment feature using PowerShell.

It is important to clarify that in the EMC (Exchange Management Console, for Exchange Server On-Premise) or in the ECP (Exchange Control Panel, for Office 365) it is not possible to perform this task.

This command applies to both Exchange Server On-Premise and Exchange Online in Office 365.

Add-MailboxPermission -Identity [email protected] -User [email protected] -AccessRight FullAccess -InheritanceType All -Automapping $false