Re: [Exim] Temporary defer on callouts

--On Saturday, January 31, 2004 10:22 am +0000 David Woodhouse
<dwmw2@???> wrote:

> On Fri, 2004-01-30 at 16:41 -0800, Bill Moseley wrote:
>> I'd like to deny on timeout/temporary error, but I think that might be
>> too extreme. So, I'm wondering if it would be possible to somehow give
>> a temporary error, but cache the event and if they try again in an hour
>> or longer then accept.
>>
>> The idea is that spammers may not try again on a temporary error, but
>> legitimate mail would try again.
>>
>> Is something like that possible -- or even a good idea?
>
> It's possible but not trivial to implement, and I'm not sure it's
> necessary.
>
> I do sender verification callouts, without defer_ok. It _does_ give a
> temporary error on timeout/temporary error -- like for example if you
> tried to send mail to me while your only MX host mail.hank.org was down.
>
> For legitimate mail you're right that they'll try again later -- but
> _also_, it tends to be the case that they'll to want to fix their own
> incoming servers when they break.

Sadly, for some of the larger mail hosts this simply isn't true. We have
periods when we can't deliver mail for days on end to providers like
hotmail, tiscali, freeserve, and so on. We've recently enabled sender
callback, and now (during those periods) receiving mail from those domains
can take several days.

The question is will our users be tempted to switch to hotmail (etc) in the
belief that it is our servers that are problematic?

--
Ian Eiloart
Servers Team
Sussex University ITS