What is Spam?
SPAM is the use of mailing lists to blanket usenets or private email boxes with indiscriminate advertising messages. Very bad netiquette. Even worse, it's bad business. The future of marketing online is about customizing products and information for individual users. Anyone who tries to use old mass market techniques in the new media environment is bound to fail.
The below are the steps to avoid a SPAM if you have not MASS MAILED or sent UNSOLICITED MAILS to others. If you have done so and started getting SPAM. Then there is little that can be done to avoid it. Your domain may to be terminated as it puts heavy load in the mail server.
Ways to Prevent Spam
 USE A SPAM FILTER
While there is no such thing as a perfect filter, anti-spam software can help keep spam at manageable level. If you are linux customer, please enable SPAM Assassin in your cPANEL.
 DON’T POST YOUR ADDRESS ON YOUR WEBSITE
It seems like a good idea at the time, but posting your email address on your personal home page is just an invitation to spammers. Spammers and the people who sell spamming as a business have software that "harvests" email addresses from the Net. This software crawls through the Internet seeking text strings that are [email protected] When it finds one, it catalogs it on a database of other email addresses to be used to send spam.
 USE A SECOND EMAIL ADDRESS IN NEWSGROUPS
Newsgroups are the great email address gathering ground for spammers. If you post to a group, you’re going to get spam -- it is just a matter of time. So how are you supposed to participate? Use a different email address than the one you use for talking to friends and relatives. In other words, have a public address and a private address. You’ll just have to deal with the spam in your public account.
 DON’T GIVE YOUR EMAIL ADDRESS WITHOUT KNOWING HOW IT WILL BE USED
 NEVER RESPOND TO SPAM
Oh sure, they say they’ll take your name off the list, but they’re lying. What they really want to do is confirm that they’ve got a live address. Also, if you respond, they’ll sell your address to every other spammer on the planet meaning you’ll soon be flooded with even more spam.