New users unable to send/receive email

I created a new user on an SBS2003 machine through the Add a User Wizard but he is unable to send or receive email outside of the domain.  He can send and receive it internally.  We checked the CALs and discovered they were near their limit and installed 5 more but that does not seem to have solved the problem.  The people who were originally set up are working fine but any new users encounter this same issue.  When email is sent to these new users it is bounce back with this error message: "The message reached the recipient's e-mail system, but delivery was refused.  Attempt to resend the message.  If it still fails, contact your system administrator.
#5.2.1 smtp;550 5.2.1 <jdoe@xxx.com>... Mailbox disabled for this recipient"
When I create new test users, they do not receive the initial server email, but all other internal emails flow properly.