Autodiscover automatically maps a mailbox for which a user has full access permissions. This can cause performance issues when opening Outlook depending on the mailbox size. If you want to grant full access to a mailbox but don’t want the mailbox to automap, you can use PowerShell to achieve this.

First, to check who currently has access to the mailbox, you can use Office 365 Admin Center or PowerShell.

Get-MailboxPermission –Identity user1@domain.com

To grant full access permissions to a user with automapping disabled, type the following command:

Add-MailboxPermission –Identity user1@domain.com –User user2@domain.com -AccessRights FullAccess -AutoMapping $False

The above command will grant User2 full access to the mailbox of User1 without automapping the mailbox.

To remove full access permissions, use the command below. This command will remove the full access permissions that User2 has over the User1 mailbox.

Remove-MailboxPermission –Identity user1@domain.com -User user2@domain.com -AccessRights FullAccess