[HLUG] Exim 4.50 on Debian 3.1 external greet_pause?

[John Hedges]

On Mon, Jan 29, 2007 at 04:01:44PM +0000, Mark Broadbent wrote:
> 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. Maybe I am less than bomb-proof. However I'm still not
convinced that the (im)probability of receiving mail from a broken
sender when your primary is down warrants maintenance of a second mail
server. Perhaps it's a bit hard line but it's better not to pander to
broken/misconfigured senders. You never know, it might prompt them to
get their servers fixed :) And as far as the warning messages are
concerned, aren't they useful to the sender? 

If your secondary can deliver mail, then fine - it's obviously useful in
that you are improving availability, but just to spool seems pointless
to me.

Cheers

John