How does ICS clear orphans from the workgroupshare.mdb database?

We create an AD account for all students and faculty at our institution - but still many do leave campus without using our mail services

I am attempting to clear out all the orphans - but it appears that we still are re-building mailboxes for persons no longer in the OU identified in the ICS configuration
The user does not exist in AD - the \users\username folder has been deleted - but when mail is received (old mailing lists, etc) a new mailbox is created again

I have made a copy of the workgroupshare.mdb file for examination and sure enough it contains several accounts for users long removed from Active Directory

How can we cleanly remove ALL deleted and/or inactive users and purge mailboxes for accounts who have never logged in
Does "lastlogin.exe" accurately indicate those accounts which have never been used?

Find Orphans does not indicate these users