Redmond has just issued a bug report informing that iOS 6.1 devices have been found to severely slow down Exchange servers, and recommends system administrators to either block it altogether or devise a custom throttling policy for iOS 6.1 users.
As of right now, the only way to fix the issue is a software update, but Microsoft has also posted three different workarounds for system administrators to make sure their Exchange servers live through the day. The advisory states:
“When a user syncs a mailbox by using an iOS 6.1-based device, Microsoft Exchange Server 2010 Client Access server (CAS) and Mailbox (MBX) server resources are consumed, log growth becomes excessive, memory and CPU use may increase significantly, and server performance is affected”.
The above page also includes additional information about the bug along with several workarounds the company has posted, so make sure you go over it if you are a system administrator.
One option is to remove and re-create the device partnership and hope for the best.
If this fails to do the job, then administrators are recommended to create a custom throttling policy for iOS 6.1 users. A last case resort to deal with the issue is to completely block iOS 6.1 users for the time being — until Apple fixes this issue in a future update.