Slashdot Mirror
I am the Most Spammed Person in the World
jefp writes "In November 2004, Microsoft's second-in-command Steve Ballmer made some headlines by mentioning that Chairman Bill Gates was getting four million spams per day. At the time, I was dealing with a little spam problem of my own - I was getting around a million spams per day. I found it a little comforting that my problem wasn't quite as bad as Bill's. However, a couple of weeks later Ballmer corrected himself, saying he mis-remembered the stat and Gates actually gets four million per year.
This means I was getting one hundred times as much spam as Bill Gates.
I've written a tutorial explaining why I get so much crapmail and how I deal with it."
he just went from 1 million a day to about 1.3 million a day.
you don't post your email address to farmgirls.com!
Give a man a fish and he'll eat for a day. Teach him to fish and he'll wipe out the species.
...but not with one slashdotting.
He's really just using Slashdot to break his server farm so he won't have to get spam anymore.
You can only be young once, but you can be immature forever.
Just yesterday I enabled Greylisting in OpenBSD spamd, and today I got 6 spams, compared with my usual 150. (per day).
It's easy to set up and works with your existing mail server. OUr mail server is qmail on red hat, but openbsd just ahppily redirects the legit (what it suspects might be legit rather) to the mail server. The load has dramatically decreaed on the mail server.
/* oops I accidentally made a comment, sorry */
Your name in the posting is a link that resolves directly to your email address.
Don't know what you're doing right now to reduce the spam, but maybe putting your email address on the front page of Slashdot is a step in the wrong direction.
There are 2 kinds of people in this world. Those that can keep their train of thought,
I dont get nearly as much spam as that, but even a few hundred a day is pretty irritating. My solution is to delete all email as soon as I get it.
I figure if its important I'll get a phone call.
air and light and time and space
Ha! I'm the World's Greatest Dad, and I have a mug to prove it!
The funny thing is, I don't have any kids....
WTF? Over?
I think the line
kinda gave that away already.
If you disagree, post your argument. (-1, Overrated) isn't your personal censorship tool for views you don't like.
Mail Filtering
Or, how to block a few million spams per day without breaking a sweat.
© 2005 by Jef Poskanzer.
Introduction
In November 2004, Microsoft's second-in-command Steve Ballmer made some headlines by mentioning that Chairman Bill Gates was getting four million spams per day. At the time, I was dealing with a little spam problem of my own - I was getting around a million spams per day. I found it a little comforting that my problem wasn't quite as bad as Bill's. However, a couple of weeks later Ballmer corrected himself, saying he mis-remembered the stat and Gates actually gets four million per year.
This means I was getting one hundred times as much spam as Bill Gates.
Nevertheless, after filtering we both get about the same amount: around ten spams per day in our inboxes. Ballmer says that Microsoft has an entire department dedicated to protecting their mailboxes from spam. At ACME Labs there's just one guy, one server, and a T1 line. And yet my filters are a hundred times as effective as Microsoft's. How do I do it?
These pages will show you how, and help you deploy similar filters on your own system.
Goals
What am I trying to do here?
Results
For those who like to read the end of a novel first, here are some overall stats showing how the filters are performing.
Environment
This is all based on a Unix system running sendmail. If you're not using Unix, or you're using a different Unix-based mail system, most of the specific advice here will not help you. You may still find some value in the general ideas.
Sendmail Config
The first layer of spam defense is sendmail itself, because that's the first piece of software to touch each message. Sendmail has a number of different config options that can help you block spam and keep your machine stable.
greet_pause
As of version 8.13, sendmail added an anti-spam feature called "greet_pause". It is both simple and clever.
In a normal SMTP transaction, first the client connects, then the server sends back a "220" greeting message, then the client sends its HELO command. Some spam programs, however, don't wait for the greeting message. They just send their commands immediately without listening.
The greet_pause feature detects this misbehavior by pausing briefly before sending out the "220" greeting message. If any commands arrive during that pause, then the connection is marked bad and anything coming over it is ignored.
This one is interesting because it actually cuts down on the number of spam attempts, not just the spam deliveries. I figure when the spammers hit the pause they are somehow getting stuck. I'll have a graph of this later - before I enabled greet_pause, I was getting a couple million spam attempts per day; after, only 600,000.
To enable the feature, you need to make two changes. First, in your sendmail.mc file:
You probably already have access_db defined; it just needs to appear somewhere prior to greet_pause. The number is how many milliseconds to pause; 5000 = five seconds. Then in your access file you should add this:
The second change prevents the pause from applying
so I sent him an email asking for the text
This guy's SMTP server:Pipelining is turned on for untrusted hosts. Nice.
Either way, a good portion of the spam hitting my system never even makes it to EHLO/HELO time because if there's any sort of resolution problems with the dns/rdns or if the hostname contains the IP address in it (RFC violation) I delay the connection 20 seonds before the greeting. RFC states clients WILL NOT send data unless asked to do so, except for pipelining which is not advertised for untrusted hosts. When the MTA sees a bunch of incoming crap, it drops the connection because they violated the RFC rules for handshaking (clients MUST wait for the greeting). This does not affect legit MTAs with temporary problems.
I go through a whole bunch of other checks even before DATA time, delaying at each step if there's a problem. 90% of the spam/viruses never even make it to scanning for spam/viruses because they violate something before that and the connection get drops (or they drop it from waiting). Once again, delaying 20 seconds does NOT affect legit MTAs.
Big writeup on SPAM filtering
My MTA
Laws do not persuade just because they threaten. --Seneca
I use my Senator's email address. I suspect he needs a bigger penis anyhow.
Long Answer: The concern is the misdirected bounce. By default and in accordance with the RFC, qmail bounces messages it accepts then later decides it can't deliver back to the sender. Spammers use false return addresses, so you end up bouncing spam back to innocent third parties. When used with naive spam-filtering techniques, this can be a problem i.e. qmail accepts the message, but a spam filter rejects it, and it is bounced. Here's what SpamCop.net has to say about it:
Everything anti-spam is done by people other than djb. I love qmail, but it really isn't the easiest server to set up for spam control. One needs about a dozen patches to get it working right.- None can love freedom heartily, but good men; the rest love not freedom, but license. -- John Milton
Hardware info here. It's a 3.2 GHz P4. I was struggling along on a 450 MHz box until only a year ago, but finally had to upgrade.