Apple's iOS 6.1 update introduced some improvements to Siri and LTE compatibility, but for many users, it also cut their phones off from 3G networks or Microsoft's Exchange. The former issue has hopefully been addressed with a bug fix, but the latter apparently remains unsolved — and Microsoft is now telling Exchange administrators they may need to block or throttle iOS 6.1 users to keep their servers running well.
"Apple and Microsoft are investigating this issue."
In a bug report, the company acknowledges that "when a user syncs a mailbox by using an iOS 6.1-based device, Microsoft Exchange Server 2010 Client Access server and Mailbox server resources are consumed, log growth becomes excessive, memory and CPU use may increase significantly, and server performance is affected." Some users, meanwhile, get error messages blocking them from accessing Office 365 Exchange Online. For now, "Apple and Microsoft are investigating this issue," and administrators are urged to open a support ticket if they're having trouble.
While the bug is being fixed, Microsoft has also given admins a few workarounds. Chiefly, iOS 6.1 users shouldn't process Calendar requests, and devices getting error messages should be restarted. If this doesn't solve the problem, though, Microsoft also suggests either re-linking the Exchange account, reducing server load by throttling iOS devices, or simply blocking iOS 6.1 users from Exchange. Apple fixed its connectivity problem fairly quickly, so it's possible an Exchange-focused update will also be coming soon. For now, though, it's a major blow to enterprise iOS users.