Dear legit sender,
this mailserver uses greylisting
as a means to fight spam. This might delay the mail you send to our domains
by a few minutes (or hours) on first contact. You don't need to do anything.
Your mailserver will just re-send. (If it's a good mailserver,
it will re-send from the same IP address.)
talking to the greylisting and greyscanning smtp daemon we run here
gives you a pretty good chance of getting trapped
and ending up on several blacklists.
All you need to do is try to deliver mail to an address we both
know in advance does not even exist in any of our domains. Should
you get tired of inventing the garbage yourself, feel free to
reuse any of the spam trap
that other spammers have used before. Come on, do it.
Prove to us that you are nothing but a spamming machine
so we can stutter the whole SMTP dialogue only to reject
the message anyway and eventually blacklist you.
Pleased to be wasting your time, sir.
Dear mail server admin,
this server is an MX for a few domains.
We run a greylisting SMTP daemon (specifically, OpenBSD's spamd
in front of the real SMTP daemon. The GREY connections are fed to greyscanner
and we let it blacklist (almost) everything that differs significantly
from the few valid addresses in these domains, known in advance.
Feel free to use the list of currently trapped hosts
as a supplement to your bigger blacklists. It is generated from the
database every night.