[gentoo-user] Sendmail confused by network change

[Bas Zoutendijk]

Dear Gentoo Users,

On my  new Gentoo laptop  installation I recently  installed Sendmail in
order to receive messages from Cron on the root account.  I noticed that
when I connect my laptop to a different network than the one I connected
to during booting,  Sendmail does not know what to do with the Cron mail
any more.

For the purpose  of clarity,  let’s say the host name  of this laptop is
‘hostname’.  I  did not  configure the  domain  part  of  the  host name
because of the mobile nature of this machine.

When  I  boot at  home,  Cron  sends  mail  to root@××××××××.homedomain.
‘homedomain’ is automatically added to all host names on my home network
by the router.  It can only be resolved inside the network;  it is not a
registered domain name.  I can receive mail from Cron just fine.

When I boot  at work,  Cron sends mail to  root@hostname.  Note that the
domain name  ‘workdomain’ is not added  to the  host name.  I  can still
receive  Cron  mail.  However,  when  I  take  the  laptop  home without
rebooting and connect to the home network, Sendmail is unable to deliver
the Cron  mail for root@××××××××.homedomain  and sends  notifications of
this  to  root@××××××××.homedomain,  which  somehow  do  seem  to arrive
without problems.  The error message  is “config error:  mail loops back
to me”.

Based on what I can find about this error on the internet, it looks like
Sendmail does not  know where hostname.homedomain is and  asks my router
to resolve that.  When it finds out it is localhost, it thinks something
is wrong and  does  not  deliver  the  mail.  A  possible solution is to
register hostname.homedomain as an alias of hostname or localhost, but I
would rather  not do that,  since hard  coding domain names  on a laptop
seems kludgy to me.

Does anyone know  a more elegant solution?  Some way  to inform Sendmail
about changes  to the domain name,  or  configure it to  check for these
changes?  I  would rather  not have  to reboot.  Restarting  Sendmail is
acceptable, I guess, but perhaps not the most elegant solution.

Sincerely,

Bas

-- 
Sebastiaan L. Zoutendijk | slzoutendijk@×××××.com