Dumb Newbie

[Jwp]

Well after a fresh install of postfix, setting my inet_interfaces = all and
restarting postfix has allowed me to telnet to port 25 with the linux box
itself, through localhost and I was also able to connect a telnet session
from another box on my lan to port 25.  Also I gained a new error on the
message that was returned:

  Recipient address: usr at b-dub.org
  Reason: Remote SMTP server has rejected address
  Diagnostic code: smtp;554 <usr at b-dub.org>: Relay access denied
  Remote system: dns;b-dub.org (TCP|167.206.5.68|52577|24.44.190.85|25)
(cosmo.b-dub.org ESMTP Postfix)


Is this a good sign?  Or is this a sign that my ISP is stopping the mail?
Cosmo.b-dub.org is the name of the server box, it does not have a mx or a
record, should I set one up?
The only forwarded port (well related to postfix) is port 25 through the
linksys router do other ports need to be opened?

Thanks,
JP