[HLUG] Exim 4.50 on Debian 3.1 external greet_pause?

[Mark Broadbent]

On 29/01/07, John Hedges <john at drystone.co.uk> wrote:
> > >The backup  should deliver
> > >immediately when the primary is up not to mention that other delivery
> > >agents should direct deliver to the primary when it is reachable (note
> > >that I leave out spammers tactics to deliberately deliver to
> > >secondaries as the anti-spam/AV measures are usually less there).
>
> Could someone explain why it is useful to have a secondary MX routing
> through the primary. If the primary is down then mail is queued on the
> secondary - without the secondary, surely the mail would be queued on
> the sending host (or returned, depending on their own policy)? It seems
> like a lot of effort for very little advantage.

Well that's the point of a secondary, to provide a spool in the event
of the primary going down or being inaccessible, not for load
management (for this you would define two mail servers at the same MX
priority).  Doing this guards against the danger of badly configured
or misbehaving sending hosts that do not or cannot resend/retry, plus
it prevents senders from seeing warning messages when the email has
been delayed.

> [...]

Thanks
Mark

-- 
Mark Broadbent
* http://www.wetlettuce.com/