[ale] postfix / Bellsouth as ISP [Solved]

[Greg Freemyer]

Thanks Mike,

Your answer is much appreciated.

Greg
On Mon, 2004-06-07 at 17:26, Mike Murphy wrote:
> Its because of this:
> 
> [mike at kermit mike]$ dig mail.bellsouth.net
> [snip]
> ;; ANSWER SECTION:
> mail.bellsouth.net.     5597    IN      A       205.152.59.17
> mail.bellsouth.net.     5597    IN      A       205.152.59.16
> [snip]
> 
> [mike at kermit mike]$ dig mail.bellsouth.net MX
> [snip]
> ;; ANSWER SECTION:
> mail.bellsouth.net.     1585    IN      MX      0 mx00.mail.bellsouth.net.
> mail.bellsouth.net.     1585    IN      MX      0 mx01.mail.bellsouth.net.
> [snip]
> 
> [mike at kermit mike]$ dig mx00.mail.bellsouth.net
> [snip]
> ;; ANSWER SECTION:
> mx00.mail.bellsouth.net. 10424  IN      A       205.152.59.32
> [snip]
> 
> [mike at kermit mike]$ dig mx01.mail.bellsouth.net
> [snip]
> ;; ANSWER SECTION:
> mx01.mail.bellsouth.net. 10395  IN      A       205.152.59.33
> [snip]
> 
> Note that the addresses returned for mail.bellsouth.net's A name (aka 
> the canonical name) are different than those returned when one queries 
> for the MX(s).
> 
> What does that mean here? Well, it seems that BS has configured those 
> hosts that are the MXs to only take mail destined for BS users, and 
> reject everything else (which is a sensible precaution, otherwise they'd 
> be open relays barring some other security precautions). The host that 
> replies to the A name for that service will pass along mail for anyone 
> (but I suspect only for hosts on the BS network).
> 
> Why do the brackets help? They tell Sendmail and Postfix to not look up 
> the MX to relay the mail, but to use the address returned with the A 
> record instead. It doesn't bother many of their users because they are 
> using a mailer client that's not an MTA, so all sane clients don't care 
> what the MX is, they just do "normal" name resolution. Sendmail and 
> Postfix (and the like), on the other hand, prefer MX hosts first in many 
> operations.
> 
> Mike
> 
> 
> Greg Freemyer wrote:
> > It worked, thanks a lot.
> > 
> > Can you explain what the issue was?  
> > 
> > ie. I have no idea what '[x.y.z]' does different from 'x.y.z'.
> > 
> > Thanks
> > Greg