On Fri, February 13, 2015 10:57, Ken Smith wrote:> Hi All,
>
> I'm just wanting to check that my understanding of the settings is
> correct as my web searches are finding a lot of dated information.
>
> If I want a Centos 6 sendmail system act as the secondary MX for
> domain
> bbbbb.co.uk do I just add a
>
> Connect:bbbbb.co.uk RELAY
>
> statement into /etc/mail/access and restart sendmail
>
> Obviously I have the DNS MX records for the domain are already
> established.
>
> I've been getting "/config error/: /mail loops back to me/ "
errors.
>
> I think I may be stumbling into a variant of cname problem where the
> hostname as far as the sendmail machine is concerned is aaaaa.com but
> the DNS setting for the secondary MX is smtp1.bbbbb.co.uk.
>
> They both resolve to the same IP but when sendmail looks up the MX
> records for bbbbb.co.uk it will find smtp.bbbbb.co.uk and
> smtp1.bbbbb.co.uk listed and it may relay the mail off to
> smtp1.bbbbb.co.uk without recognising that aaaaa.com >
smtp1.bbbbb.co.uk. Am I on the right track here, as I then just need
> to
> change the secondary MX setting in DNS to aaaaa.com?
When I set up secondary MX services in Sendmail (and Postfix) then I
always use the direct address feature of the domain routing table and
avoid looking up MX RRs altogether. After all, if the mail arrived
here it is a good bet that the main MX is off-line (or this is
SPAM/UCEM but that is another issue).
So assuming that the primary MX host is mx10.example.com and the
secondary is mx40.something.else then with Sendmail the file
/etc/mail/mailertable on mx40.something.else should contain something
like this:
example.com. esmtp:[mx10.example.com]
.example.com. esmtp:[mx10.example.com]
The [] brackets prevent MX lookups and just routes the message traffic
directly to mx10.example.com as soon as a connection can be made.
This prevents the most common source of mail loops where the primary
is off-line and so any mail is bounced back to the backup MX, which
just happens to be the host that just sent it, thus causing the loop.
--
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