On Fri, Jun 12, 2015 at 10:24:28PM -0700, PGNd wrote:
> I don't want to lose mail if the back-end server connection is
> offline for an extended period of time.
If the expected maximum downtime for the backend system is well
below the positive cache time on the frontend, you can ignore the
possibility of backend downtime. Once the cache is primed with
all the addresses that routinely receive email, the backend system
is not needed to validate incoming email.
Otherwise, there's only one correct solution: Automate replication
of recipient validation tables from the backend system to the
front-end system. Stop using recipient verification probes, and
just use local (replicated) tables on both systems. Anything else
has warts. You can tweak the exact manner in which you lose, but
you can't not lose.
--
Viktor.
