Full mailbox access permission and account automapping are a great exchange features. Automapping was introduced in Exchange 2010 and basically uses autodiscover to automatically map all mailboxes in Outlook to which a user has full access permission. Automapping was a boon for Exchange admins who no longer had to walk users through the process of adding accounts after granting full access permission in outlook via: Outlook Profile > More Settings > Advanced > Add.
Unfortunately if when running Outlook in Cached Mode (which is the default), all data within each additional account a user has automapped will be synced to the users local OST file. Since the preconfigured OST file size limit in Outlook 2010 and 2013 is 50GB, this can pose challenges. One thing you can do as a sysadmin to prevent OST corruption is to check the size of the mailboxes before granting full-mailbox access in a cached environment. If the aggregate of the automapped users plus the main users mailbox is greater than 50, it’s not a good idea if you’re running Outlook 2010. Outlook 2013 and 2016 have built in functionality to only sync partial mailboxes, so in those environments size isn’t as important.
Ok so let’s say we didn’t check the mailbox size for user with automapped accounts and now he’s saying that Outlook 2010 just keeps syncing and never finishes. Upon inspection you find the user has 5 mailboxes automapped and they are definitely close to or even over 50GB combined. What can you do?
- Remove full access permissions for for the user from the accounts.
- Delete the users OST file and re-generate it. OST files are like databases, they do not shrink in size after you remove automapped accounts. If you’re at or close to the 50GB limit with an OST, I recommend re-creating it after removing full access permissions for as many other mailboxes as possible.
- Note that in some environments (even Office365) removing full mailbox access may not immediately remove the automapping. In that instance, here’s how to disable automapping for that user with a powershell command.
The powershell command below disables Automapping for Mark Steele after granting him full mailbox access to user Jane Smith.
Add-MailboxPermission -Identity Jane.Smith -User 'Mark.Steele' -AccessRight FullAccess -InheritanceType All -Automapping $false