Spam has become so insidious that every company has to consider the cost and means of reducing its impact. Sometimes it’s as simple as implementing a basic spam filter and applying best practices– i.e., following a few rules for recognizing and eliminating spam. On the other end of the spectrum are the most aggressive tactics, which involve turning the tables on spammers. This article provides ten tips to help eliminate spam email from your inbox.

1. Use Spam Filters.

When email was originally designed in SMTP (Simple Mail Transfer Protocol) there was no reason to authenticate email message senders because email was originally only for trusted users such university researchers. So to make the process simpler, emails were designed to be able to “hop” from one machine to another, on to its destination. On the public Internet, this is a serious flaw [1], allowing spammers to spoof the origin of a message.

Initially, spam filters were created that used a dictionary method to filter spam if certain words were present (e.g. “Viagra” or “Sex”). It was not until years later, that IronPort (recently acquired by Cisco) devised a more robust, effective spam filtering method using a two-layer defense model [1], now used in over 20 percent of email servers.

Outer Layer: Reputation Filter
The outer layer is a reputation filter that uses a variety of factors to decide how trusted a particular sender of an email is. The email filter gets the factors needed to check a particular sender from a single global database called SenderBase:

1. SenderBase collects email traffic data comes from over 100,000 networks, allowing sending patterns of mail servers to be tracked and detected.
2. It measures over 150 parameters including email send and receive quantities, IP sending age, country, etc., to establish a score for each IP address.
3. Mail from trusted IPs is passed through to anti-virus scanners, while bad senders are blocked.
4. Those emails that remain, namely questionable senders, are then sent to layer 2.

Inner Layer: Context Analysis
Layer 2, the inner layer, is known as Context Analysis, and acts like a search engine, scanning the contents of your email in order to answer some questions related to its legitimacy:

1. Who sent the email message?
2. Does it have suspicious attachments (based on any current virus outbreaks)?
3. Does it have embedded hyperlinks to known bad domains?
4. How was the email constructed?

Read more at: http://www.itsecurity.com/features/email-inbox-security-011107/