Apples recent release of iOS 6 .1 has caused some stir in the exchange community. A bug in this release causes a calendar request that was previously approved then modified and then approved again from an iOS 6.1 device to be rejected by exchange the
device continues to send the update over and over again causing large transaction log growth for the exchange database where the mailbox is located.
As a work around until Apple releases a fix you can implement an ActiveSync Device Access Rule:The following examples will create the 4 necessary access rules for blocking all iOS 6.1 Devices.
New-ActiveSyncDeviceAccessRule -querystring "iOS 6.1 10B141" -characteristic DeviceOS -accesslevel block
New-ActiveSyncDeviceAccessRule -querystring "iOS 6.1 10B142" -characteristic DeviceOS -accesslevel block
New-ActiveSyncDeviceAccessRule -querystring "iOS 6.1 10B143" -characteristic DeviceOS -accesslevel block
New-ActiveSyncDeviceAccessRule -querystring "iOS 6.1 10B144" -characteristic DeviceOS -accesslevel block
!!UPDATE !!
The 6.11 update does not fix this issue. This update is specifically for iPhone 4s devices and addresses signal issues.
As for removing these rules after an update is released. After an update is released you do not want to remove the rules as this would allow non-updated devices to hit your exchange system again. The rules I posted above are a specific to 6.1 iOS version. If you have iPhone 4s users you will need to add another rule for the 6.11 as it also will cause the same issue as 6.1 and the rules above will not block it. to prevent 6.11 iPhone 4s devices from connecting use this rule:
New-ActiveSyncDeviceAccessRule -querystring "iOS 6.1 10B145" -characteristic DeviceOS -accesslevel block
These rules do not accept wildcards, so when an update is finally released that fixes the issue if users update to that release they should be automatically allowed to connect again.