 devrandomI got a pot, full of random stuff herePremium
join:2003-06-28 | Postgrey for Postfix MTA out From the same guy who created Mailgraph, DWS.. today released on postfix-users his newest tool, Postgrey (Postfix Greylist Policy Server).
Located here for the interested: »isg.ee.ethz.ch/tools/postgrey/
In a nutshell, what Greylisting [def] is supposed to accomplish is basically taking advantage of how mailservers generally follow RFCs, and how sloppy spammers don't.
In the normal process of sending mail you normally have something like this..
User-> Sending MTA -> Recipient MTA -> User
But this is what happens if the Recipient MTA is down for some reason (network outage perhaps) or somehow says "come back later".
User -> Sending MTA -> Can't reach Recipient MTA -> Deferred and holding mail for later
Now, what greylisting depends on is getting unlisted, unknown IPs to resend the mail like any sane RFC compliant (and fault tolerant) MTA would do to establish a kind of "trust relationship".
So right after
User -> Sending MTA -> Can't reach Recipient MTA -> Deferred and holding mail for later
It would go try again..
User -> Sending MTA -> Recipient MTA -> User
and that would work technically.
In the case of a spammer, it would go something like this..
User -> Sending MTA -> Can't reach Recipient MTA -> ???
Of course, you're thinking right now..what if spammers follow the RFC and just send the mail again?
The thing here is that greylisting depends on unknown IPs to say "come back later, I might let you in then," which the advocacy site at that point in time proposes that it'll be caught by spam filters anyway (possibly external filters like Razor).
This in fact is a very "shaky ground" situation, but maybe just an annoyance tool at best in the MTA administrator's arsenal of toys, bats, clubs and ninjas.
I personally won't use it, but just thought it might be nice to bring another tool into the eyes of administrators out there everywhere. Its a nice tool, just maybe not for everybody.
Anybody want to chime in on what they think the usefulness of greylisting will be?  |
 jester121Premium
join:2003-08-09
Lake Zurich, IL
 ·voip.ms
| I'd say questionable at best. Anyone whose server sends to hotmail knows how overloaded their SMTP servers get; I frequently see messages sit in queue for a couple hours before they get sent without timing out.
And based on the amount of junk that shows up in my hotmail account, even with their blocking efforts, I'd question whether or not this is worth the effort. |
