/etc/resolv.conf and sendmail

[Alexander Dalloz]

Am Mi, den 14.07.2004 schrieb Gene Heskett um 19:15:

> I was under the impression that it was a localmail problem all along, 
> (like amanda trying to send root a message) in which case mail sent 
> to AAA, must have the AAA defined in the hosts file, or as an entry 
> in a dns record in some machine known to AAA.  The point being that 
> if AAA is unknown, then the dns of record (from resolv.conf) is going 
> to be consulted for the resolution of the address represented by AAA.
> 
> At least thats how I've understood it for over a decade now.
> 
> Sorry if I was mistaken, and please educate me if you have the time.

> Cheers, Gene

Hi Gene,

I am myself a current learner and far from "knowing that all".

Let me try to move through the things from a different route. By default
first the /etc/hosts file is asked for name resolution. That is defined
in the /etc/host.conf with content "order hosts,bind". If the hosts file
does not hold the information then a nameserver will be asked. These are
defined in the /etc/resolv.conf. The possible "search foo" syntax in
there says: if the given name to be looked up is not a FQDN then add the
given foo domain to the name first for lookups.

The /etc/hosts file maps IP addresses to FQDN (fully qualified domain
names) and their short names to IP addresses. In Philippe's case the AAA
is no short name but his internal local domain name. But the hosts file
does not resolv domain names, it resolves fully qualified domain names,
which are hostname + domain name. In his case P4.AAA is the FQDN and P4
the short name.

Speaking about mail it is correct that mail sent to outside must come
from a host with a resolvable FDQN (must, because most MTAs reject
unresolvable relays to prevent SPAM). Host internally sent mail uses
localhost or as FQDN localhost.localdomain as relay and lookup that in
the hosts file (therefor you see the comment in there).

Of course, if Philippe did give his Sendmail a hostname which is not
resolvable, neither by the hosts file nor a DNS, his MTA will not work
proper. So I requested him to paste the results from "sendmail -bt
-d0.12 < /dev/null" to get closer to his configuration.

Alexander


-- 
Alexander Dalloz | Enger, Germany | GPG key 1024D/ED695653 1999-07-13
Fedora GNU/Linux Core 2 (Tettnang) Athlon CPU kernel 2.6.6-1.435.2.3.uml
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