1. Guard your address carefully.This should go without saying. But people often disclose their e-mail addresses without a second thought. Once your address is out, it's out for good.Think twice before giving out your e-mail address at stores. You may sign up for notices of special offers and sales, and, in turn, the store wants your e-mail. Most stores should have an iron-clad privacy policy. But even e-mail you opted to receive starts looking like spam if you receive too much.Don't post your e-mail address on the Web. Spammers use automated programs to scour the Web for addresses. Don't include your e-mail address in forum postings. What's the point? Let members respond online.Your company's contact page could be your biggest dilemma. You want your customers to contact you easily. But how do you stop spammers from contacting you just as easily?Hiding your address in an HTML tag won't do the trick. Spammers will find it. Also, you might have seen addresses like this: joeblow(NOSPAM)@joeblow.com. This used to work, but spam bots are getting smarter. So stay a step ahead.One solution is to include your address as an image. It's legible to the human eye. But spam bots can't read it — for now, anyway.You can also use JavaScript to display your e-mail address. The script renders your address in HTML when the page is loaded. Visitors see the address and can click it to send a message. But spam bots won't see it. You can see a sample script at the following site: http://joemaller.com/js-mailer.shtml.You can also use a contact form on your Web page. Customers fill out the form, which is sent to you. The e-mail address is not revealed. As some bloggers have learned, however, this may generate "comment spam."

2. Use multiple addresses.It's a good idea to use multiple e-mail addresses. I have a personal one for friends and family. I have instructed them not to disclose it to anyone or to forward messages to it. As an added precaution, I use an approved list so I only get messages from addresses I specify.I have a second address when I request information. I only check it when I'm expecting something. It mostly gets spam.I have a third address for shopping. Receipts and shipping confirmations are sent to this address. Spam doesn't matter. Likewise, if I forget to opt out of marketing mailings, it doesn't matter.My work address poses the biggest problem. I need to receive all legitimate mail sent to it. And spam can be a real time-stealer. Unfortunately, I don't know who will be sending me e-mail or when. So an approved list won't work.

3. Use disposable addresses.Disposable addresses have become popular. This may be a more manageable alternative to maintaining multiple accounts.Some services, such as Mailinator (http://mailinator.com), allow you to make up an e-mail address without registering. The address is created when a message is sent to it. These services aren't appropriate for sensitive e-mail. With no password, anyone can read the messages.You can also use services that require you to register in advance. Spamgourmet (http://www.spamgourmet.com) and Sneakemail (http://www.sneakemail.com) are two. You create an e-mail address that forwards e-mail to your regular account. The disposable addresses expire automatically or you can delete them.If you have your own mail system, you can create your own disposable addresses. Simply use an address until it is overloaded with spam, then retire it.

4. Consider private domain registration.Many people forget their contact information sits online, ripe for harvesting and accessible by anyone. It's the contact information you provide to your domain registrar. A Whois search will reveal this quite quickly. It's a handy source for determined spammers.You're required to provide valid information when you register for your domain name. Spammers know this. So they know the e-mail addresses are good.One option is to change your e-mail addresses frequently. Do this through your registrar, then cancel the old e-mail address. That way, there's a valid address for good e-mail. But you stay a step ahead of the spammers.You might consider private domain registration. Several registrars offer this at an additional charge. Your contact information is replaced with the registrar's information. Instead of your e-mail address, the registrar's address is displayed. Before you consider this, research how it handles legitimate e-mail sent to the address.Recent FTC reports indicate this threat may be negligible. However, you may not want to take the risk. Once a spammer gets your address, you'll soon be buried under an avalanche of spam.

5. Use a challenge-and-response system.People who use challenge-and-response systems invariably speak highly of them. One person I spoke with said he hasn't received spam in his inbox since he started using one such system.Here's how it works: You install software that integrates with your e-mail program. When the program connects to the server to download e-mail, it checks messages against your approved list. Addresses in your contact list are automatically approved. You can approve others manually.Approved messages are downloaded to your computer. A challenge e-mail is sent in response to other messages. Once the sender responds to the challenge, the original message is downloaded. Future messages from the sender pass through unchallenged.The system works because spammers can't respond to the challenge e-mail. Spam is generated by computers with little or no human intervention. E-mail addresses are spoofed. Or they're sent by zombie networks, compromised computers controlled by spammers.There is one problem. You could miss messages you want to receive. Some people complain that the system is rude because legitimate senders must do the work. Others refuse to cooperate by responding. You risk losing customers who decline to participate.Further, in some cases, a response is all but impossible. For example, I send millions of opt-in newsletters each week. If 10% of my subscribers used a challenge system, I'd receive hundreds of thousands of challenges. I'd have to hire additional staff to deal with the influx, and even then it would be difficult.Popular challenge and response solutions are Qurb (http://www.qurb.com), Vanquish Anti-Spam (http://www.vanquish.com), and WinAntiSpam 2005 (http://www.winantispam.com). All services in 2005 ranged in price from $25 to $40.

6. Implement adaptive filters.A couple of years ago, creating effective filters was easy. Keywords and addresses could be added to a blocked list. But spammers adapted quickly. Now, static filters have questionable effectiveness. Spammers spoof addresses and use creative spellings to trick filters (p0rn and V-I-A-G-R-A are classic examples).Adaptive filters are much better. Programs that employ Bayesian filtering are proving effective in blocking spam without false positives that block legitimate messages.Bayesian filters learn by watching you. They compare messages you mark as spam with ones you allow. They analyze the words contained within the messages, along with clues such as formatting. The filter scores messages based on content and handle them appropriately. Unfortunately, they often require extensive training.FireTrust's MailWasher Pro (http://www.firetrust.com), G-Lock Software's SpamCombat (http://www.glock.com), and Symantec's Norton AntiSpam (http://www.symantec.com), all feature Bayesian filtering. (Costs for these services were up to $40 in 2005.)Similar spam-blocking products and services use scoring systems. But the spam characteristics are aggregated from other users. They do not specifically adapt to you. Their effectiveness probably won't be so good.