[Greylist-users] stats from big sites?

[Brian Grossman]

I can provide some statistics for softhome.net.  We had our own greylist
implementation in place a few days before the last big windows worm (I
forget it's name).  Greylist saved us from the bulk of that.  It also saved
us much pain when osirusoft and others succumbed to DDoS attacks.

We accept several hundred thousand incoming messages per day.  I don't
have statistics handy for how many we refuse.  Our greylist implementation
is python+mysql+qmail.  Mysql 4.0.x on linux 2.4.x.  The greylist table
is an innodb table, currently apx 8 million rows (a little over 8GB for
data+indexes).

The admin staff noticed a drop in spam after we turned it on.  The spam
went back up a bit after osirusoft died.  I personally still get several
hundred spam messages a day, most of which spamassassin catches.

Myisam doesn't handle the high volume of inserts and updates well, thus
innodb.  The database load grew over the first month then tappered off.
The database quickly outgrew it's disk space, then struggled under
I/O load.

Most of our users have accepted greylist without complaint, probably not
even noticing it.  Of those who do notice and complain about the delay,
most are happy to put up with the delay after we point to a FAQ about it.
Others need to receive email quickly and either upgrade to a pay account so
they can control it or presumably leave.

The most common way people learn about it is when mail servers send the 451
message back to the sender saying the message was delayed.  Many people
"can't" read those and assume the message is outright lost.  Sometimes, the
mail servers don't give a good error message, not even passing along our
451 message.  Sometimes the mail servers misinterpret the 4xx as a 5xx, but
that's already been discussed on this list.  Occasionally, we've run into a
site that will bounce a message after just a couple temporary failures.

If you're going to do a trial run, I suggest you put some volunteers on it
and run the others in learning mode for a month and a half.  That should
give you an idea of resource requirements and give you an idea of user
experience.

One other suggestion for user experience: let end users adjust the color of
the entry (black, white, grey, etc) and add and delete entries.  It can
then also be used as a general purpose black/white list.

Our python code for greylist is available by request.

Brian