How to Survive Anti-Spam Filters

Anti-spam filters catch every incoming email before it is delivered into the Inbox and review it. They use a scoring system to classify an email as spam or legitimate. These filters (you might have heard about SpamAssassin, SpamProbe, or SpamCombat) look for certain patterns in the message, and assign "spam points" to it based on certain criteria: words, phrases, or even colors.

Depending on what these filters find or don't find in the message, points are added to or taken away from a scoring system. If the message score is 5.0 or higher, the filters add the *SPAM* word to the subject line of the message and the email is redirected to a bulk or junk mailbox. The lesser the score, the better.

So, one of the main concerns when designing an email newsletter is to ensure that it will pass an anti-spam test. Here are a few tips you may follow:

1. Check what you put in the subject line

The Subject line is usually carefully examined. For example, if you type a recipient's name in the message subject like To: [recipients name], your message will get 2.86 points because of this. If there is a lot of free space in the subject line, the email gets 2.64 points added to the score. The word FREE written in caps weighs additional 1.10 points.

If you put a date into the subject line, you can take off 0.48 points. And you can take one full point off if your subject contains a newsletter header!

2. Keep your message size from 20K to 50K

The size of the message does matter for anti-spam filters. The majority of spam emails are less than 20K. So, you can actually get 0.71 taken from your score if your message in within the 20K to 50K range.

3. Be wise with CAPS

If you use too many capital letters in your message, you'll get 0.21 points added to your score. So, use them wisely!

4. Use full hyperlinks

If you use a hyperlink in your email, make sure you put the http:// at the beginning. A spam filter will add 1.28 points to your emails if you don't!

5. Be restrained with colors

Colors do matter too. Blue adds 0.21 points, red 0.33 points, and Magenta 0.44. The background color other than white adds 0.317 points to the message score. The Black is optimal as it won't add or take any points off.

6. Be a welcome guest

Send email only to people who have opted in at your site. This will help in the case if you need to prove you are not spamming, and that people do want to receive the emails from you.

Do not send to a list harvested or purchased on the Internet because:

  • Those people don't know you and they don't expect emails from you. So, they can use the "Report Spam" button to stop future mailings from you. After a number of spam complaints, the ISP will block your IP address.
  • Email lists sold on the Internet contain many bad and old email addresses. Old email addresses are often used as spam traps. It means that no one should email to such addresses. If someone sends a message to a spam trap account, this attempt is classified as spam and the sender's IP address is blacklisted. If you are blacklisted for some reason, contact the server provider immediately.

7. Test your email placement

Use G-Lock Apps delivery and spam testing tools to test your Inbox placement, spam scores, and authentication issues. G-Lock Apps also provides daily blacklist monitoring to check if your server’s IP address is blacklisted and sends you summary email alerts if any problems are detected.

8. Don't use spammer e-mail software

Anti-spam filtering systems are aware of some favorite email programs that professional spammers use and they add on as many as 3 points if you send the messages with those programs. Be sure to check the ISPs hit list to see what email software are on it.

Remember that anti-spam filters are not perfect and they often happen to be over protective. They can give false negatives and false positives results after the message analysis. A false negative is when a pure spam email gets through the filter, and a false positive is when a legitimate email ends up in the junk box flagged as spam.

Around 150 companies now offer spam filtering software. The number of anti-spam techniques is growing and anti-spam technology is getting smarter. For example, some servers (challenge systems) send an email back to the original sender and require a reply before they forward the email to the recipient. The idea behind this is that only a human can reply to a request for specific information. America Online recently announced a new spam filter that can actually learn the preferences of each of their subscribers.

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