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
