The Hostway Blog

Guide to Spam Filters

When left unchecked, spam clutters email inboxes making it difficult to locate important communications, and can carry nefarious programs such as various viruses, Trojans, and worms. A spam filter is a software program that can be installed on a network server, mail server or personal computer. This software sorts out junk mail before it even hits the inbox and has a chance to possibly infect the system with malicious code.

There are a number of types of spam filters available for commercial and personal use. Spam software can be coded to filter based on Bayesian analysis, blacklisting, rules and challenge response among others. After learning about the different types, you will be better equipped to choose the right one for your business.

Types of Spam Filters

  • Rules-based filters: These filters use user defined rules to block emails. The user may create a rule to block out a specific sender or all emails with a specific word in the subject line or body.
  • Header filter: Email headers contain information about the identification and location of the sender. Sometimes those sending spam will send emails with falsified header information. A header filter stops all emails that it analyzes and determines to have a false header. The problem is that not all spam emails have falsified headers. This type of filter may let a lot of spam to the inbox.
  • Content filters: These are coded to analyze the content of a message to determine whether it is spam or not. This is a powerful type of filter, but can filter out emailed articles and newsletters that you actually want to receive.
  • Permission filters: All email not specifically authorized by the user is blocked by this type of filter. This can be advantageous for businesses with highly sensitive information that may have severe legal or security ramifications if compromised.
  • General blacklist filter: This type of filter stops all emails considered on a general blacklist. Whitelist email addresses originate from sources known not to engage in sending spam. Whether you use this type of filter or not, it is a good idea to find out if your business is somehow on the blacklist. This may occur if you regularly send out promotional emails or electronic newsletters. You can apply for whitelist inclusion.
  • Challenge-response: This filter requires a sender to enter a code displayed as an image on a Web page. The purpose is to ensure that an actual human is sending the email and not a spam software program.
  • Bayesian filter: A very powerful filter that learns what you consider spam. It then uses advanced technology to analyze all incoming messages to determine the statistical probability that they are spam based on prior experience.

Choosing any of these to protect your business is better than having none at all. Prices are very affordable and they are relatively easy to install.