On Fri, Jun 10, 2011 at 09:35:03PM +0200, Wiebe Cazemier wrote:
> > It can't. Never before seen recipients will be deferred, recipients
> > validated while the primary MX was up and cached (for 7-14 days) will
> > however be accepted. This is good enough, and the best you can do
> > without getting a recipient feed from the primary MX host.
> >
>
> Not considering spam, a backup MX cannot know any user on the primary
> MX, ever, because the only time it will try to verify the recipient
> address is when the primary is down. Otherwise mail won't be sent to it.
The spammers will do a good job of probing the target address space.
Otherwise, arms-length backup MX is a relic of the past, and the best
solution is to stop offering the service.
--
Viktor.
