Am Fr, den 09.07.2004 schrieb Rodolfo J. Paiz um 18:26:
> >>>I use define(`SMART_HOST',`[mail.bellsouth.net]') in
> >>>sendmail.mc. This has been working well since long before FC2.
> >>
> >>Why the Bellsouth SMTP server in squared brackets?
> >
> >I haven't seen that done in SMART_HOST, but in mailertable the square
> >brackets mean that the host is the actual SMTP host. Without them,
> >sendmail does a DNS lookup on the name looking for an MX record, assuming
> >that the name is an email domain, not a particular host.
>
> So in theory then, when we *know* that a given hostname is the MX record
> for that domain then we can put its name in brackets and save two DNS lookups?
Yes, for Sendmail you prevent/forbid MX lookups by putting a host
address (name or IP) into squared brackets. But you should be really
sure to which host you "force" it.
> Rodolfo J. Paiz
If you do host lookups you can see that mail.bellsouth.net is not the MX
for mail.bellsouth.net, so probably special mail servers for the own
customers.
$ nslookup mail.bellsouth.net
Server: 192.168.0.1
Address: 192.168.0.1#53
Non-authoritative answer:
Name: mail.bellsouth.net
Address: 205.152.59.16
Name: mail.bellsouth.net
Address: 205.152.59.17
$ host -t MX mail.bellsouth.net
mail.bellsouth.net mail is handled by 0 mx01.mail.bellsouth.net.
mail.bellsouth.net mail is handled by 0 mx00.mail.bellsouth.net.
;; ADDITIONAL SECTION:
mx00.mail.bellsouth.net. 10377 IN A 205.152.59.32
mx01.mail.bellsouth.net. 10377 IN A 205.152.59.33
So the MX hosts for bellsouth.net have different names and IPs than
mail.bellsouth.net.
Alexander
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