Exch 2k NDR rcpts been deltd no eml addr

ISSUE: sporadically receive a NDR on messages send from either with-in exchange domain, or from outside smtp clients to any exchange recipients that says “The recipient has been deleted or has no e-mail address” in every case the email address to is good. You can resend the same email a little bit later and it will go through fine.

WHAT I WANT: explain why exchange sends the bogus message (What is really triggering the error message) and second: what I can do to resolve it.

Server: Compaq 1600 1.2GB Ram, Raid 5, plenty free disk space, processor runs average 17%, Exchange 2000 server latest service pack on SBS 2000 server SP4.

Bonus points to good answers