Re: [Exim] Callout timeouts: opinions sought

On Fri, 20 Aug 2004, Ian Eiloart wrote:

> quoting David Woodhouse:

> > If they reject after RCPT TO:<someuser@domain> that's probably a bogus
> > user so I'd like to drop any mail claiming to be from that user.
>
> Yes, me too.
>
> > If they reject after MAIL FROM:<> then they're clueless _and_ they've
> > probably been provoked into doing so by receiving a lot of bounces to
> > mail they didn't send... they're probably being joe-jobbed a lot. So
> > it's a fairly good chance the mail I'm being offered is fake and hence I
> > also want to drop it.
>
> Again, me too.

I'm convinced that I've seen an MTA respond OK to MAIL FROM:<> , and
then respond to the RCPT TO with a diagnostic which rejected the null
sender address. Yup, here's an example:

[...] sender verify fail for <TacK@???>: response to "RCPT
TO:<TacK@???>" from smtp.ole.com [213.4.129.130] was: 550 5.7.1
Remitente vacio no permitido. Empty sender not allowed.

It's uncommon, but it does happen.