Mail forwarding is bypassing MX record and going straight to local

I'm trying to help my web/mail hosting company figure out an issue.
Can anyone give me a real quick answer on reasons a sendmail smtp
server would not do an MX look-up when forwarding mail?

Here is my setup:

My domain has an A record and MX record that point to my sendmail smtp
server. (hosted by another company for me)

So when someone sends email to me @mydomain it comes to the correct
server, of course.

That server @mydomain is configured to forward mail to my specific
email address (I can't move the MX record because some addresses
@mydomain don't forward) to my address at another domain. Lets say
the other domain is @anotherdomain.

The MX record for @anotherdomain point to the other mail server
located at a different hosting company. The A record however does
point to the @mydomain, because we have a web-site using that same
domain that is hosted by that company.

For several years now, up until about a week ago, it has been working
"correctly" and the sendmail server @mydomain was using the MX record
and correctly forwarding email to the server that the MX record
pointed to for @anotherdomain. Now, all of the sudden (I'm not sure
what changed), the server is not respecting the MX record and is
instead just sending it over to the "local" server that hosts are
@anotherdomain web-site.... I'm not sure if it is because it started
using the A record for the DNS look-up instead of the MX record, or if
some setting got changed and now it isn't even looking for the MX
record because it "thinks" it should handle mail for that domain.

Lets assume it isn't easy for me to move domains around or change
hosting companies.... so I'm looking for some sendmail setting (in a
config file?) that might cause this to happen. Any ideas?

Re: Mail forwarding is bypassing MX record and going straight to local

In article
<7f2d2853-a222-4643-b695-f1a2efe3b453@y5g2000hsf.googlegroups.com>
eselk@surfbest.net writes:
>
>For several years now, up until about a week ago, it has been working
>"correctly" and the sendmail server @mydomain was using the MX record
>and correctly forwarding email to the server that the MX record
>pointed to for @anotherdomain. Now, all of the sudden (I'm not sure
>what changed), the server is not respecting the MX record and is
>instead just sending it over to the "local" server that hosts are
>@anotherdomain web-site.... I'm not sure if it is because it started
>using the A record for the DNS look-up instead of the MX record, or if
>some setting got changed and now it isn't even looking for the MX
>record because it "thinks" it should handle mail for that domain.

Most likely the latter. I lost track somewhere in your description of
who was supposed to be forwarding where, but a common cause for this is
that you need to use confDONT_PROBE_INTERFACES - see cf/README.

--Per Hedeland
per@hedeland.org

Re: Mail forwarding is bypassing MX record and going straight to local server?

In article
<7f2d2853-a222-4643-b695-f1a2efe3b453@y5g2000hsf.googlegroups.com>,
eselk@surfbest.net wrote:

[...]

> For several years now, up until about a week ago, it has been working
> "correctly" and the sendmail server @mydomain was using the MX record
> and correctly forwarding email to the server that the MX record
> pointed to for @anotherdomain. Now, all of the sudden (I'm not sure
> what changed),

Um, that's a problem. Something changed, and it shouldn't be hard to at
least look at config files (e.g. sendmail.cf, resolv.conf, nsswitch.conf
)if you are running such a system) etc.) and see what changed. If that's
not revealing, you may have a severe system management problem.


> the server is not respecting the MX record and is
> instead just sending it over to the "local" server that hosts are
> @anotherdomain web-site.... I'm not sure if it is because it started
> using the A record for the DNS look-up instead of the MX record, or if
> some setting got changed and now it isn't even looking for the MX
> record because it "thinks" it should handle mail for that domain.

Sendmail does not ignore MX records. It can be configured to route mail
in arbitrary ways that don't use MX records, such as smarthosting, but
it won't just use an A record where an MX is present.

> Lets assume it isn't easy for me to move domains around or change
> hosting companies.... so I'm looking for some sendmail setting (in a
> config file?) that might cause this to happen. Any ideas?

It seems far more likely to be a problem rooted in the resolver config
of the operating system or in the DNS records that Sendmail is seeing.

--
Now where did I hide that website...

Re: Mail forwarding is bypassing MX record and going straight to

On Nov 21, 1:50 pm, es...@surfbest.net wrote:
> I'm trying to help my web/mail hosting company figure out an issue.
> Can anyone give me a real quick answer on reasons a sendmail smtp
> server would not do an MX look-up when forwarding mail?

Thank you Per and Bill. Turned out to be this file:

/etc/mail/mailertable.virtual_domains

Our hosting company removed the domain name in question from this
file, and now sendmail does an MX record and correctly forwards mail
for that domain to the other server.

They managed to break something else though, but that is another story
for another day, and I don't have enough details on the NEW ISSUE yet.
=[