There are two databases in Exchange that are important.
One is the IS - the Information Store. This holds all of the e-mail
messages, and allows them to be viewed by mailbox.
The other is the DIR - the Directory. This holds a list of all users of the
Exchange system.

As long as both directories have been restored, then things should be OK.
BUT BUT BUT if you are doing ANY restores of Exchange, you must read and
understand the Microsoft Disaster Recovery for Exchange white paper. It is
available on the Microsoft web site, or via TechNet etc. This will explain
exactly how to install NT and Exchange in order to allow a restore of the
information.

Cheers,
Chris Jordan
CMG UK Ltd.