[RndTbl] Shaw dropping bounces?

[Trevor Cordes]

We just noticed something strange:

Shaw's mail server appears to be dropping some bounces.

Our setup is, on Shaw cable ISP, running our own mail server, with Shaw's 
mail server as our smarthost.  Our MX is to our own (Shaw dynamic) IP, so 
we can recieve mail directly.  The reason for this messed up config is 
that Shaw 1-2 years ago started blocking outgoing SMTP, but they don't 
block incoming SMTP.

If you have a similar setup (some of you must), try sending email to:

bogususerid at valid.domain.com

and

bogususerid at bogusdomain.com

(fill in the "bogus*" with something you make up)

The 1st (valid domain) one will bounce.  The remote mail server (outside 
of Shaw) will bounce back to you.  No problem there.

The 2nd (invalid domain) one will not bounce.  It will just disappear.

My current theory is Shaw's mail server is wanting to bounce the 2nd one 
but looks up the MX and thinks "hey, this is in my ISP IP space" and "no 
one there is allowed to run a server" and then dropping it.

Any other ideas?