[ale] postfix / Bellsouth as ISP [Solved]

[Mike Murphy]

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

-- 

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Mike Murphy
781 Inman Mews Drive Atlanta GA 30307
Landline: 404-653-1070
Mobile: 404-545-6234
Email: mike at tyderia.net
AIM: mmichael453
JDAM: 33:45:14.0584N  84:21:43.038W
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+