TweetFollow Us on Twitter

Review: SpamAssassin

Volume Number: 19 (2003)
Issue Number: 6
Column Tag: Reviews

Review: SpamAssassin

Regaining Control of your Inbox

by Vicki Brown

Ready, aim, fire!

Separating the Wheat from the Chaff

The popularity of the Internet, plus increases in connectivity (and email access), has given rise to a corresponding avalanche of spam. We all know what spam is - unsolicited junk email offering goods or services that we don't want, don't need, and often didn't want to know existed! We all agree that we would like less of it. Failing that, how can we wade through it, manage it, and delete it without losing our desirable mail (or our minds) in the process?

Many "solutions" have been proposed to deal with the spam problem. These range from anti-spam filters integrated inside email applications (e.g., the junk mail filters in Apple's Mail) to standalone products of various levels of complexity, ease of use, effectiveness, and cost.

My current solution of choice is SpamAssassin (http://www.spamassassin.org), in combination with procmail (http://www.procmail.org). I post-process the results through my desktop email client, (Eudora), for a very powerful and accurate spam-killing solution.

SpamAssassin provides many features, including:

  • user-configurable spam score threshold

  • ability to re-write Subject lines

  • user-configurable filters, using Perl regular expressions

  • modification of existing Spam scores

  • use of statistical, "Bayesian" analysis

  • "auto-learning"

  • optional use of DNS blacklists (e.g., Real-time Blackhole List)

  • optional use of Network Checksum Tests (services that compare message checksums to known spam)

  • "whitelists" (From addresses that are considered OK)

  • Accepted message languages

Note that SpamAssassin and procmail both run on the server side (where mail is originally delivered), not on the client side (i.e., usually not on the desktop) and neither has a GUI front end or a particularly "user-friendly" configuration mode. If you, or your users, are not technically inclined, I recommend that you choose a different path. However, if you enjoy tinkering, have some understanding of regular expressions (e.g., you've used Perl) and like to work with text-based configuration files, you will find the SpamAssassin/procmail combination to be powerful, flexible and, more important, accurate.

Configuration

SpamAssassin comes pre-configured with a large set of tests that it will perform on all incoming mail. In addition, you can add new tests, skip tests, raise or lower the "score" assigned by a given test or, using procmail, cause some mail to skip SpamAssassin altogether. Goto http://www.spamassassin.org/doc.html to see more detailed documentation. You'll even find a pointer, at that URL to a SpamAssassin configuration generator tool, designed to make it easier to customize an installation of SpamAssassin with some common options.

Much of the power of SpamAssassin comes from its configurability, its use of Perl regular expression pattern matching, and its interaction with procmail.

For example, many spammers have started adding ever-changing sets of numbers to the ends of subject lines, to fool the simpler junk mail filters. One GUI-based anti-spam application I tried had a set of filters designed to try to catch mail of this form. The filters looked like this:

   if Subject ends in 0
or if Subject ends in 1
or if Subject ends in 2
...
or if Subject ends in 9

This is rather cumbersome; worse, it doesn't handle the spammers who throw in a space at the very end. SpamAssassin's approach is both shorter and more flexible. This regular expression matches any digit, followed by 0 or more whitespace characters, at the end of the Subject line.

Subject =~ /\d\s*$/

SpamAssassin's interaction with procmail also allows me to specify whether mail is even sent through the SpamAssassin filters. For example, I can specify that mailing list messages should be delivered directly. This procmail recipe checks the message headers for one that matches the given Reply-to string, sending mail from the SpamAssassin-Talk list to my pre-defined default mailbox, without further processing.

:0 H
* ^Reply-to:.*spamassassin-talk
$DEFAULT

Results

SpamAssassin doesn't actually delete any spam. Instead, it tags each piece of mail it processes with a set of headers, e.g.,

X-Spam-Status: Yes, hits=6.2 required=2.5
tests=AWL,CLICK_BELOW,FREE_TRIAL,HTTP_WITH_EMAIL_IN_URL,
spam_PHRASE_05_08,VLB_spam_OFFER_4,VLB_TO_NOT_NAME,WEB_BUGS
version=2.43
X-Spam-Flag: YES
X-Spam-Level: ******
X-Spam-Checker-Version: SpamAssassin 2.43 (1.115.2.20-2002-10-15-exp)

X-Spam-Flag is a simple Boolean; if a message is considered potential spam, the flag is set (and the value is YES). X-Spam-Level provides more information; one "*" is given for each integer value of the spam score. X-Spam-Status provides full scoring information as well as which tests passed. Note that some tests raise the spam score while others are designed to lower it. After all tests have been run, the resulting score is compared to a (user configurable) threshold. If the score exceeds the threshold, the message is tagged as spam.

The user gets to decide how to handle the mail after it's been processed and tagged. One possibility is to continue processing with procmail. For example, the SpamAssassin docs assert that mail with a score of 15 or higher is almost certainly spam (with 0.05% false positives, according to SpamAssassin's rules/STATISTICS.txt file). After some use, I decided to lower this cutoff even more. I have configured procmail to delete any mail tagged with a Spam score of 10 or higher, using the following recipe:

:0:
    * ^X-Spam-Level: \*\*\*\*\*\*\*\*\*\*
    /dev/null

Other than that, all remaining mail is delivered. I have occasionally found false positives in mail with scores of less than 10; I want to check that mail by eye.

Here's where my third tool comes in. I use Eudora as my mail application and make extensive use of Eudora's filter mechanism to post-process my potential spam. I separate potential spam by mailboxes and labeling, based on certain criteria such as whether the message contains my full name (or only my email address), how high the spam score is, and any other interesting criteria. I scan the "Junk" mailboxes a few times a day, pull out false positives (setting new filters to catch those the next time!), and trash the real junk.


Installation

This is only a review, not a tutorial, so the installation section will hand wave a lot. You'll need a server machine running some variant of *nix (e.g., FreeBSD, Linux, or Mac OS X). If your server runs Mac OS X, you'll need to make sure it has been configured to deliver mail locally (e.g., using sendmail or qmail). How to set up a server is beyond the scope of this review.

You should also note that, although SpamAssassin can be run without procmail, its flexibility (and power) increases when it is used in conjunction with procmail. SpamAssassin does not include code to handle local mail delivery; it relies on procmail (or something else) for delivery. Unless you know that a reliable "something else" is available, use procmail.

Procmail may already be on your server; it is pre-installed on most *nix systems these days (use whereis procmail or locate procmail to check, then read the documentation to determine how to configure procmail for your server situation). If it's not pre-installed, download and build procmail from the procmail.org web site.

SpamAssassin is probably not pre-installed on your system; however, installation is simple. In fact, you'll probably be able to install it without first downloading the archive. SpamAssassin is written as a Perl module; the easiest way to install it is by using Perl's CPAN shell (from the command line, as root):

perl -MCPAN -e shell 
o conf prerequisites_policy ask
install Mail::SpamAssassin
quit

Alternatively, you can always download the latest archive from spamassassin.org, then build and install SpamAssassin according to the documentation. If you have any problems, be sure to read the Installation notes on the SpamAssassin site. Check the documentation for more information on configuration, as well as useful options.

Summary

If you're looking for a powerful, flexible, and accurate solution to the spam problem, I recommend that you consider the team of SpamAssassin and procmail. Both programs are free and come with example recipes and suggestions for how to use them to your best advantage. Each has a support community that you can draw upon for assistance and ideas, as well as mailing lists to keep you informed. If you have a server on which to install it (note that SpamAssassin can be installed server-wide or on a per-user basis) and know (or are willing to learn about), regular expressions, SpamAssassin may be the spam-killing tool you've been looking for. Give it a try.

References


Vicki Brown

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Latest Forum Discussions

See All

Six fantastic ways to spend National Vid...
As if anyone needed an excuse to play games today, I am about to give you one: it is National Video Games Day. A day for us to play games, like we no doubt do every day. Let’s not look a gift horse in the mouth. Instead, feast your eyes on this... | Read more »
Old School RuneScape players turn out in...
The sheer leap in technological advancements in our lifetime has been mind-blowing. We went from Commodore 64s to VR glasses in what feels like a heartbeat, but more importantly, the internet. It can be a dark mess, but it also brought hundreds of... | Read more »
Today's Best Mobile Game Discounts...
Every day, we pick out a curated list of the best mobile discounts on the App Store and post them here. This list won't be comprehensive, but it every game on it is recommended. Feel free to check out the coverage we did on them in the links below... | Read more »
Nintendo and The Pokémon Company's...
Unless you have been living under a rock, you know that Nintendo has been locked in an epic battle with Pocketpair, creator of the obvious Pokémon rip-off Palworld. Nintendo often resorts to legal retaliation at the drop of a hat, but it seems this... | Read more »
Apple exclusive mobile games don’t make...
If you are a gamer on phones, no doubt you have been as distressed as I am on one huge sticking point: exclusivity. For years, Xbox and PlayStation have done battle, and before this was the Sega Genesis and the Nintendo NES. On console, it makes... | Read more »
Regionally exclusive events make no sens...
Last week, over on our sister site AppSpy, I babbled excitedly about the Pokémon GO Safari Days event. You can get nine Eevees with an explorer hat per day. Or, can you? Specifically, you, reader. Do you have the time or funds to possibly fly for... | Read more »
As Jon Bellamy defends his choice to can...
Back in March, Jagex announced the appointment of a new CEO, Jon Bellamy. Mr Bellamy then decided to almost immediately paint a huge target on his back by cancelling the Runescapes Pride event. This led to widespread condemnation about his perceived... | Read more »
Marvel Contest of Champions adds two mor...
When I saw the latest two Marvel Contest of Champions characters, I scoffed. Mr Knight and Silver Samurai, thought I, they are running out of good choices. Then I realised no, I was being far too cynical. This is one of the things that games do best... | Read more »
Grass is green, and water is wet: Pokémo...
It must be a day that ends in Y, because Pokémon Trading Card Game Pocket has kicked off its Zoroark Drop Event. Here you can get a promo version of another card, and look forward to the next Wonder Pick Event and the next Mass Outbreak that will be... | Read more »
Enter the Gungeon review
It took me a minute to get around to reviewing this game for a couple of very good reasons. The first is that Enter the Gungeon's style of roguelike bullet-hell action is teetering on the edge of being straight-up malicious, which made getting... | Read more »

Price Scanner via MacPrices.net

Take $150 off every Apple 11-inch M3 iPad Air
Amazon is offering a $150 discount on 11-inch M3 WiFi iPad Airs right now. Shipping is free: – 11″ 128GB M3 WiFi iPad Air: $449, $150 off – 11″ 256GB M3 WiFi iPad Air: $549, $150 off – 11″ 512GB M3... Read more
Apple iPad minis back on sale for $100 off MS...
Amazon is offering $100 discounts (up to 20% off) on Apple’s newest 2024 WiFi iPad minis, each with free shipping. These are the lowest prices available for new minis among the Apple retailers we... Read more
Apple’s 16-inch M4 Max MacBook Pros are on sa...
Amazon has 16-inch M4 Max MacBook Pros (Silver and Black colors) on sale for up to $410 off Apple’s MSRP right now. Shipping is free. Be sure to select Amazon as the seller, rather than a third-party... Read more
Red Pocket Mobile is offering a $150 rebate o...
Red Pocket Mobile has new Apple iPhone 17’s on sale for $150 off MSRP when you switch and open up a new line of service. Red Pocket Mobile is a nationwide MVNO using all the major wireless carrier... Read more
Switch to Verizon, and get any iPhone 16 for...
With yesterday’s introduction of the new iPhone 17 models, Verizon responded by running “on us” promos across much of the iPhone 16 lineup: iPhone 16 and 16 Plus show as $0/mo for 36 months with bill... Read more
Here is a summary of the new features in Appl...
Apple’s September 2025 event introduced major updates across its most popular product lines, focusing on health, performance, and design breakthroughs. The AirPods Pro 3 now feature best-in-class... Read more
Apple’s Smartphone Lineup Could Use A Touch o...
COMMENTARY – Whatever happened to the old adage, “less is more”? Apple’s smartphone lineup. — which is due for its annual refresh either this month or next (possibly at an Apple Event on September 9... Read more
Take $50 off every 11th-generation A16 WiFi i...
Amazon has Apple’s 11th-generation A16 WiFi iPads in stock on sale for $50 off MSRP right now. Shipping is free: – 11″ 11th-generation 128GB WiFi iPads: $299 $50 off MSRP – 11″ 11th-generation 256GB... Read more
Sunday Sale: 14-inch M4 MacBook Pros for up t...
Don’t pay full price! Amazon has Apple’s 14-inch M4 MacBook Pros (Silver and Black colors) on sale for up to $220 off MSRP right now. Shipping is free. Be sure to select Amazon as the seller, rather... Read more
Mac mini with M4 Pro CPU back on sale for $12...
B&H Photo has Apple’s Mac mini with the M4 Pro CPU back on sale for $1259, $140 off MSRP. B&H offers free 1-2 day shipping to most US addresses: – Mac mini M4 Pro CPU (24GB/512GB): $1259, $... Read more

Jobs Board

All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.