[Mailman-Users] mailman w/ fedora 7

[Tamakh]

I'm having a problem with only external email servers trying to send to my
list.  I can send email to the listserv  list from the same box, but not
outside.  I keep getting the following error that I'm guessing either
sendmail or something else on the box is blocking:


Delivery to the following recipient failed permanently:

    test at myurlhere.com <test at listserv.bloomfield.org>

Technical details of permanent failure:
PERM_FAILURE: SMTP Error (state 13): 550 No such user.


Any ideas please?

Thanks!
-Tam