[afnog] sendmail problem

[Brian Candler]

On Wed, Nov 08, 2006 at 10:26:52AM +0200, Alex Gondwe wrote:
>    I have two DNS servers for the Local area network.
>    When Internet connection is interrupted, the DNS servers are still
>    able to do resolution for the local domain.
>    As expected, resolution for all external domains fails.
>    At this point the mail server is able to accept mail for the local
>    domain from the Local area network.
>    If I try to send mail to an address that does not belong to our local
>    domain, the server fails to receive the mail.

OK, so the mail server is doing DNS checks on the recipient address (RCPT
TO) before accepting the mail.

IMO this is incorrect behaviour for an outbound mail relay, whose job it is
to accept mail from the client as quickly as possible, and then deliver it
at its leisure.

There's almost certainly a way to reconfigure sendmail to skip this test.
But since fewer and fewer people use sendmail these days, you may have to
ask on a specialist sendmail list to find out how.

You could start with looking at the m4 macro-based configuration system,
which has quite a comprehensive README I think. If you can find a suitable
macro then add it to your .mc file, rebuild a new .cf from that, and use it.
Sorry I can't give any more specific info.

>    I had a similar scenario with a dial-on-demand machine  running
>    sendmail. Whenever a client machine tried to send mail to the server,
>    the server would not receive mail before first connecting to the ISP.
>    To work around the problem I opted to use postfix instead of sendmail.

That's a good workaround :-)

>    In the current situation it appears that I will have to live with
>    sendmail.

Then you have to invest time and effort in learning how to workaround its
stupidity :-(

Regards,

Brian.