Re: [gentoo-user] Sendmail confused by network change

[John Covici]

On Wed, 20 Sep 2017 05:45:07 -0400,
Bas Zoutendijk wrote:
>
> 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.

Restarting sendmail seems fine with me, if you want to have something
that works everywhere, why not get a domain name from ddns or
somewhere and use a full fqdn all the time -- you can put  your home
machine on another host in that domain and you will be good to go.

-- 
Your life is like a penny.  You're going to lose it.  The question is:
How do
you spend it?

         John Covici
         covici@××××××××××.com