- When you migrate users to Exchange Server 2013, make sure that all mailboxes in a delegated relationship are moved together.
- Make sure that users who use delegated relationships are deployed in the same version of Exchange Server.
When the updated server that is running Exchange Server 2013 tries to authenticate the user, it uses a mechanism that is not understood by Exchange Server 2007. This causes the Exchange Server 2013 Store process to crash and fail over the database to a different server. Co-existence with Microsoft Exchange Server 2010 is not affected by this problem.