Learn about spammer tricks 2

MIME

A two-part Multipurpose Internet Mail Extensions (MIME) encoded message can also be an effective tool for spammers. The plain-text portion may look like legitimate mail, and be accepted by the filter. However, the HTML portion shown to the recipient contains the spammer's message. To combat this, spam filters must check whether text and HTML portions of two-part MIME messages are the same.

JavaScript

Spammers can send HTML messages with spam contained in a JavaScript that will only display the spam once the e-mail is loaded. To prevent this, filtering software needs to decode or block JavaScript.

Different headers, same spam

Another simple yet prevalent technique, spammers are sending the same e-mail content with different headers to increase their chances of bypassing filtering software.

Confusing encryption

In the business world, encrypted e-mails are often scrambled as a string of meaningless symbols and characters. Spammers have tried to replicate this by including lines of random characters in their messages. Filters may read this as encryption and accept the e-mail as coming from a trusted source.