Scotty,
I have 4 users on my mac.  3 of us use mail.  My son finally set up his account.  Now 2 accounts are unable to open.  When u click the mail icon a question mark appears, while the third account mail has vanished.  I have tried to reboot, update, delete his account all to no avail.  Help

______

This may be too involved of a problem to try to solve via email.  If they are IMAP accounts then you should be able to delete them then re-add them.  This may be better handled with an actual session.  You can schedule a session from my website or make a reservation at the genius bar at the Apple Store Southpark.    They may be able to help you as well.