Errors in Exchange mailbox permissions
The adapter might not set the mailbox permissions correctly, even though the request generates a SUCCESS message.
If multiple permissions are set in a modify request but only the last permission takes effect, you must modify the SetMailboxPermissionDelay registry key.
The SetMailboxPermissionDelay registry key cause the adapter to wait a specified time in seconds before processing the next permission. The default setting of this key is 0 or no delay. Typically setting this registry to 20 resolves the problem.
For information about setting registry keys, see Modifying registry settings.