Here's the letter which was obtained by 9to5Mac:
The Enterprise Messaging Operations team has been monitoring unusually high traffic on the enterprise mail environment originating from iOS devices running the new iOS 6.1 update. We have researched and identified a bug that causes the “iDevice” to continuously loop while synchronizing a recurring meeting invite. Some of you may notice additional side effects including poor battery life and overall degraded device performance.
The team continues to work with Apple and Microsoft to resolve the issue. However, until resolved, we’re forced to temporarily disable the ability to accept or manage meetings using any mobile device. Users will still be able to view their calendars and sendreceive email on their mobile devices during this time. Users will also continue to have the ability to manage their calendars using their normal mail clients and using Outlook Web access.
We apologize for any inconvenience this may cause – our goal is to minimize impact and disruption to the overall enterprise mail service. Please feel free to contact the Enterprise Messaging Operations team at firstname.lastname@example.org with questions.
Michael J. Freker
Notably, Vodafone today is also reporting that there is a bug with iOS 6.1 that affects 3G performance with the iPhone 4S.