Hosting mail

I'm not sure if I'm going about this the right way. 

We want to host a few mailboxes for a small company on our Domino server, 
using their Internet domain name.

If possible, I don't want them in my NAB, so I created a secondary NAB and 
use directory assistance. I created a mail file and listed it in a person 
document in the secondary directory.

Everything works EXCEPT mail delivery to this user, from the Internet.

SMTP Server: Mail for hal@xxxxxxx rejected for policy reasons.  Recipient 
could not be found in the Domino Directory.   

By everything, I mean:
SMTP mail delivery - The messages are getting to my server
Directory assistance - I can use the person document in the secondary 
directory for Web authentication
I can even use it for retrieving POP3 mail!!!!
I can send Notes mail to them using their Notes name and NRPC (not SMTP)

The only thing I can figure is that DA is not designed to work for inbound 
mail delivery. The help says DA can do the following:
1-Client authentication 
2-Group lookups for database authorization
3-Notes mail addressing 
4-LDAP service searches or referrals

Number 3 is not spelled out, but I think it is for outbound addressing 
lookups only?

If not, I guess I will create an OU for them in our primary NAB.
====================================
Tom Kreimer
Information Alternatives