Re: [exim] First time SMTP connection with "temporary error"…

Heron wrote:

> I have pointed out that some SMTP servers in the world reject incoming
> e-mails for the first time with a "temporary error" message. If the message
> comes second time it is accepted.
> This mechanism is used to reject many spams, since many spam sending
> computers do not try to send the message again after receiving "temporary
> error" message from the remote SMTP server.
>
> My question is - how to implement such mechanism in Exim 4.x ?

It's called grey listing.

I use greylstd from http://greylstd.cmeerw.org, the relevant exim.conf
part is:

   # Greylisting
   defer   message       = Greylisting in effect, please try again later.
           log_message   = greylisted.
           domains       = +local_domains : +relay_to_domains
           !senders      = : postmaster@*
           !hosts        = +relay_from_hosts
           !authenticated = *
           condition     = ${if eq 
{${readsocket{/var/run/greylstd/greylstd.sock}
{check $sender_host_address $sender_address 
$local_part@$domain\n}{60s}{}{}}}{def
er}{true}{false}}

The time is something you adjust to your liking, 5 minutes is not
unusual, even if some servers do retry fast at the start then fall back
to a more usual 15 minutes retry cycle.
--
René Berber