Last night we installed SP3 - no issues at all with the upgrade.
Today I happened to log in with our exchange administrator account .. who has been granted permission to mount any mailbox he wishes. (this was done via ADSI Edit and he was given Full Control in our Administrative Group).
In the past, he was able to mount any mailbox, on any of the domains in our forest. However, now he can not. It seems like he can still mount any mailbox, but only in the domain that he is in (we have a different domain that contains only student accounts.. no computers, service accounts, etc).
I can't seem to figure out why. If I do a Get-MailboxPermissions on an account in either domain, I see the same permissions (almost all of them are inherited permissions). When he mounts a mailbox in OWA he gets a "Your mailbox appears to be unavailable. Try to access it again in 10 seconds. If you see this error again, contact your helpdesk." And when he mounts a mailbox in Outlook 2013, the mailbox appears, but when clicking on the mailbox, he gets a "Cannot expand the folder"
Not sure if its a SP3 thing .. or if this is something that happens whenever we apply a new SP (cant remember this happening with SP2).