We recently migrated from Exchange Server 5.5 to Exchange Server 2003. Before the migration, several users who are out on leave set out-of-office messages, but now mail sent to those mailboxes doesn't generate an out-of-office message. What happened?

This is a known side effect of using the Exchange Migration Wizard. (Search the Migration Wizard documentation and you'll find a description of the problem.) When you use the Wizard to move user mailboxes, the out-of-office rule loses its link to the user's Inbox, which gets a new globally unique identifier (GUID) when it's moved during the migration. Since the out-of-office rule can't find the associated folder, the Information Store (IS) turns off the rule, which will need to be reset.

— Paul Robichaux