Fighting spam via greylisting

Bryan Kadzban bryan at kadzban.is-a-geek.net
Sun Apr 8 09:24:19 PDT 2007


Bruce Dubbs wrote:
> The systems is supposed to just give a temporary failure.

And it does -- after the RCPT TO, it gives a "450 4.7.1 <rcpt-addr>:
Recipient address rejected: greylisted, see <url>" type response.  So at
least the postgrey people were smart enough to do that.  ;-)

> Many times spammers use cut down mailers and don't retry.

Yeah, but how hard would it be to add retrying to a spammer's botnet
software?  I'm going to predict that within the next year, if
greylisting is implemented widely (and I've been hearing about it a lot,
but I don't know how many servers actually do it), the spammers will
just start retrying once if they get a temporary-error response.

But hey, for the moment, it might work.  Probably worth a try at least.

> We are only giving a temp failure message for 5 minutes.

Yes, but my ISP's mailer doesn't retry for at least 10 minutes.  The
message I sent whose date was 9:06 AM EST didn't actually get delivered
to me until 9:18 AM EST; the intervening time was the server delay.  Not
that that's bad, mind you, but I don't think it's specified either (the
delay could have been a couple hours).

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