Re: multiple relays in smtpd.conf

On Wed, Aug 02, 2017 at 02:47:27PM +0200, Christian Gut wrote:
>
> > On 2.Aug. 2017, at 14:09, Gilles Chehade <gilles@poolp.org> wrote:
> >
> > On Wed, Aug 02, 2017 at 01:47:09PM +0200, Kirill Miazine wrote:
> >> * Eric Faurot [2017-08-02 13:24]:
> >>> On Wed, Aug 02, 2017 at 11:44:47AM +0200, Christian Gut wrote:
> >>>> Hi List,
> >>>>
> >>>> is it possible to have multiple relays (you might want to say smart hosts) in smtpd?
> >>>>
> >>>> I currently use the following line:
> >>>>
> >>>> accept from local for any relay via smarthost.example.org <http://smarthost.example.org/>
> >>>>
> >>>> Now I would like to have multiple smart hosts in there for backup reasons, if one of the smart hosts is in maintainance. Is something like this possible?
> >>>>
> >>>> accept from local for any relay via { smarthost1.example.org <http://smarthost1.example.org/>, smarthost2.example.org <http://smarthost2.example.org/> }
> >>>>
> >>>> Kind Regards,
> >>>> Christian
> >>>>
> >>> It's not possible at the moment. There is ongoing work to support this feature,
> >>> along with other improvements. But it's quite a big change, and we can't give an
> >>> ETA right now.
> >>
> >> what about defining a new name in DNS containing addresses of all
> >> smarthosts as a workaround for the OP for now?
> >>
> >
> > This can work in some use-cases, this is exactly what a co-worker did to
> > work around the limitation.
>
> How will smtpd operate then? Does it use the DNS records in a round robin fashion or does it try them one after another if they fail?
>

smtpd maintains states about its routes to a destination.

what will happen is that it will resolve your relay hostname into all of
its addresses and attempts to route to them. if a route is broken, it is
marked as such for a small period and reattempted later, meanwhile there
will be routes that aren't marked as broken and which smtpd will be able
to use.


--
Gilles Chehade

https://www.poolp.org @poolpOrg