Exchange 2007 Mailbox Database Will Not Mount
I've seen this a couple of times now - so a blog post will make the solution searchable via Google for other folks to find. ;-)
I've requested that a check for this be added to ExBPA, we'll see if that happens. The error is:
Exchange is unable to mount the database that you specified. Specified database <GUID>; Error code: MapiExceptionAmbiguousAlias: Unable to mount database. (hr=0x80004005, ec=2202)
This occurs during when trying to mount a mailbox database on a new Exchange 2007 server.
This happens in a migration environment when an account having Exchange administrative privileges has a sAMAccountName but no userPrincipalname. More specifically, a specific user was delegated Exchange rights in a pre-Exchange Server 2007 environment, and had a "pre-Windows 2000 logon name" specified in ADU&C, but not a "User logon name".
There appears to be a similar issue in Exchange Server 2003, introduced by a post-SP2 hotfix. KB 932599 and KB 930241 discuss that problem.
A fairly simple solution appears to be to use the Exchange Server 2003 administration console (ESM) to determine all of the accounts that have been delegated Exchange administrative privileges and ensure that they all have userPrincipalNames ("User logon names" in ADU&C).