Anti-spam techniques (e-mail)
End-user anti-spam techniques
There are a number of techniques that individuals can use to reduce the problems associated with spam.
Enable and Configure Automatic Techniques
Many Internet service providers and e-mail clients have automated anti-spam systems installed, or can have optional systems added. Since all anti-spam techniques can cause legitimate e-mail to be incorrectly identified as spam, many anti-spam systems are either not enabled by default or are configured to be very conservative about what will be identified as spam. Automated anti-spam systems are discussed in more detail below.
E-mail Address Harvesting
Address harvesting are methods that spammers use to obtain e-mail addresses of real people, and if the spammers can't learn of the address, the address is less likely to be sent spam.
Most people want new people to be able to contact them via e-mail and many people cannot hide their e-mail addresses. While preventing spammers from obtaining email addresses does not solve the spam problem any more than avoiding the high crime areas of a city solves crime, individuals need to weigh the risks.
One way that spammers obtain email addresses to target is to trawl the Web and Usenet for strings which look like addresses, using a spambot. Contact forms and address munging are good ways to prevent email addresses from appearing on these forums.
There are other ways that spammers can get addresses, such as dictionary attacks in which the spammer generates a number of likely-to-exist addresses out of names and common words. For instance, if there is someone with the address adam@example.com, where 'example.com' is a popular ISP or mail provider, it is likely that he frequently receives spam.
Address munging
Posting anonymously, or with a fake name and address, is one way to avoid "address harvesting," but users should ensure that the fake address is not valid. Users who want to receive legitimate email regarding their posts or Web sites can alter their addresses so humans can figure out but spammers cannot. For instance, joe@example.net might post as joeNOS@PAM.example.net.invalid, or display his email address as an image instead of text. Address munging, however, can cause legitimate replies to be lost. And if it's not the user's valid address, it has to be truly invalid, otherwise someone or some server will still get the spam for it.
Contact Forms
Contact forms allow users to send email by filling out forms in a web browser. The web server takes the form data, forwarding it to an email address. The user never sees the email address. Contact forms have the drawback that they require a website that supports server side scripts. They are also inconvenient to the message sender as they are not able to use their preferred e-mail client. Finally if the software used to run the contact forms is badly designed they can become spam tools in their own right. Additionally many spammers have taken to using contact forms to send spam to the intended recipient.