Why Don't my Email Filters Work

Why Don't My Email Filters Work?

So you're being bombarded with spam emails from your website. Now you enter a list of words to for your email program (i.e. Outlook express) to look for and filter out those emails, but they don's seem to work.

Ok - let's look at an example, say you want to filter emails that contain the word:

food

You enter your filter but still the emails get through. The reason for this is the way your email program interprets the message and how the mail was sent to you.

So if you take your email with the example word 'food' and look at the source (in Outlook Express right click on the message, choose properties, the detail tab and message source tab).

You might then see something like this:

Food

Doesn't look much like the word food does it!

Now  are html comment tags so your email program ignores them and everything between them, which means it just displays the word food.

Of course your filter sees Fo<--89nshwtjq-->od and cant find a match with 'food' so lets the email through.

Don't worry there is a solution to this and it involved passing your email to a program, like Perl and it's very easy for a scripting language like Perl to pick-up and filter out stuff like this using a simple IF statement like:

if ($mail_msg =~ /[0-9a-zA-z]{1,10}[0-9a-zA-z]{1,10}/ig) {
print "found comment spam\n";
exit;
}

The above example looks for up to 10 letters (or numbers) separated by HTML comment tags.

Using simple IF statements you can also search for numbers that replace letters, such as f0od, where a zero has been used in place of the letter o.

If you're not quite up to writing Perl code yet here's something you can do now to help cut down on the amount of unsolicited mail by scrambling your email address on your web page. Just use this free tool - Instant Email Scramble.

Instant Email Scramble is about as simple as they come. Our single screen user interface has only two fields. First you enter your actual email addres. Next you give your email address a title or name which is what inserts onto your web page. Click one button, copy and paste and you’re done.

People visiting your web site will see your email address in plain English on your web page. In fact, when they click on your email hyperlink, your scrambled email address still triggers the 'mailto:' command for your visitor's email software.

The beauty of Instant Email Scramble is that you and your visitors will not notice any difference in how your email links work. But the robot email harvesters will run away empty handed!