How to Combat Spam
Everyone knows what spam is. If you have an email address (which I know you have), then you know how irritating and troublesome it is to get rid of those spam mails. Automated software that the spammers utilized can search out email addresses out in the public internet and will have spam mails sent to them. So, if you know that spam is a problem for you, what will your customers think if they receive so many spam mails? Are you prepared to counter the spam and keep your customer happy?
Local Blacklist Filters
Having a blacklist filter is not one of the more useful methods these days. Spammers are more advance that sending spam from the same email address over and over again. They randomize the email addresses and its domains, making it difficult for us to filter it using a blacklist. Blacklisting functionality is only really useful in avoiding email from other real people you don't particularly wish to hear from anymore.
Keywords and Regular Expressions
Using keywords, the system will check the email for words found within the header and body of the email and block them out if a match is found. The core problem with keyword-only filters is they can "over filter". Someone who puts "sex" on their keyword filter will find receiving local news and event announcements difficult if they live in a town named "Essex".
This is where regular expressions come in to prevent such a mistake. These are syntax rules set to identify certain strings of text or numbers. These rules can be set up to identify text patterns that are commonly used in Spam. They can become quite complex, but, as with most any filtering method, are not 100% bullet proof.
Bayesian Filters
At current, the more advanced of spam filtering system out there is the Bayesian inferences. Bayesian filters take a large data set and determine the probability a message is Spam based on its similarity to previous Spam messages. The more emails that are processed and flagged theoretically make the filter more accurate. Services that provide filtering on an ISP or host level, like Postini's "SpamAway", filter billions of emails and provide the highest level of success and fewest "false positives". SpamAway is already highly intelligent about identifying Spam and doesn't require any "learning" commands or examples be provided. The online, browser based interface keeps flagged messages in an easily accessible "quarantine" and allows the user to check for any false positives. White list functionality is provided to aide in the prevention of future false positives. A hosting company offering such an advanced service takes Spam and virus filtering for their customers seriously.
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