Simplicity and inexpensive nature of e-mail has made it one of the most preferred mode of communication even in business circles. Being the cheapest mode of communication - most people today prefer e-mail over telephone or fax. Perhaps the nearest rival to e-mail today is SMS - which has limited scope in business communication.

The rising popularity of e-mails has attracted a whole range of scamsters, professional hackers, virus writers and mail order businesses to send mass e-mails. According to one estimate, nearly half the mails circulating through Internet today are spam !

Mail Blocking By Spam Filters

Latest survey result by filtering firm MessageLabs reveals that unsolicited email messages or spam account for an astonishing 67.6% of the 841 million emails scanned during April' 2004 (source: businesseurope.com).

If half to two-third of all messages sent globally are unsolicited - imagine the financial strain on individuals and corporates who have to sift through this junk everyday. European firms are estimated to have lost US Dollar 2.5 billion dealing with junk mail.

As a result - almost all ISPs use some kind of spam filter to counter this menace. SpamAssassin is one such anti spam software - that many ISPs around the world use.

Unfortunately, spam filters block legitimate e-mails also alongwith spam. No anti-spam software can claim to block 100% spam or allow 100% legitimate mail to pass through. As a result, your legitimate e-mail may get blocked by a spam filter without you or your recipient ever knowing about it.

Deliberate Mail Deletion By Recipient

What makes an e-mail suspect in the eye of a spam filter ? You should know that and make sure your legitimate e-mails do not look like a spam. If it does - it will never reach recipient's mailbox. Worse - neither you nor the recipient will ever know about it as most spam filters do not inform the recipient about blocked mail.

Even the recipient may delete the mail without reading, if it looks like spam. Because of spam and e-mail-borne viruses - most people these days check e-mails at server and download these only after deleting suspect looking e-mails. The decision to delete an e-mail is mostly based on quick look at its header - mainly subject. So, if subject of your e-mail is a suspect - chances are it will end-up in trash folder 'un-read'

How Spam Filters Work ?

It is important at this point to learn how a spam filter works so that we can take precautionary measures to ensure our e-mails do not get blocked by it. We shall take SpamAssassin as an example

SpamAssassin works by "scoring" each e-mail message against a range of tests designed to identify if that message is spam or not. A wide number of tests are provided, including checks to see if the sender and recipient address are valid, if the message dates are valid, if the body contains any of a list of forbidden words, if any of the sending servers are blacklisted, and so on. Each test adds to a message's overall spam score; messages over a certain user-defined threshold are treated as spam and can be either trashed or marked with a special spam header.

In addition to these tests, SpamAssassin comes with a Bayes algorithm which "learns" to recognize new spam on the basis of old spam messages. This makes it possible for the software to automatically adapt and identify spam even in the absence of specific header or body tests.

In next issue, we shall discuss specific elements that make a legitimate e-mail spam suspect as also how to avoid it.