Anti-spam techniques (e-mail). Overview

(From Wikipedia, the free encyclopedia)

To prevent e-mail spam, both end users and administrators of e-mail systems use various anti-spam techniques. Some of these techniques have been embedded in products, services and software to ease the burden on users and administrators. No one technique is a complete solution to the spam problem, and each has trade-offs between incorrectly rejecting legitimate e-mail vs. not rejecting all spam, and the associated costs in time and effort.
Anti-spam techniques can be broken into four broad categories: those that require actions by individuals, those that can be automated by the email administrator, those that can be automated by e-mail senders and those employed by researchers and law enforcement officials.
End-user techniques
There are a number of techniques that individuals can use to restrict the availability of their e-mail addresses, reducing or preventing their attractiveness to spam.
Address munging
Address munging is the practice of disguising, or munging, an e-mail address to prevent it being automatically collected and used as a target for people and organizations who send unsolicited bulk e-mail. Address munging is intended to disguise an e-mail address in a way that prevents computer software seeing the real address, or even any address at all, but still allows a human reader to reconstruct the original and contact the author: an email address such as, "no-one@example.com", becomes "no-one at example dot com", for instance. Any e-mail address posted in public is likely to be automatically collected by computer software used by bulk emailers — a process known as e-mail address harvesting — and addresses posted on webpages, Usenet or chat rooms are particularly vulnerable to this. Private e-mail sent between individuals is highly unlikely to be collected, but e-mail sent to a mailing list that is archived and made available via the web or passed onto a Usenet news server and made public, may eventually be scanned and collected.
Disadvantages
Disguising addresses makes it more difficult for people to send e-mail to each other. Many see it as an attempt to fix a symptom rather than solving the real problem of e-mail spam, at the expense of causing problems for innocent users.
The use of address munging on Usenet is contrary to the recommendations of RFC 1036 governing the format of Usenet posts, which requires a valid e-mail address be supplied in the From: field of the post. In practice, few people follow this so strictly.
Disguising e-mail address in a systematic manner (for example, user[at]domain[dot]com), is just as bad as not disguising the address at all as such addresses can be revealed through a simple Google Search.
Alternatives
As an alternative to address munging, there are several "transparent" techniques that allow people to post a valid e-mail address, but still make it difficult for automated recognition and collection of the address:
- "Transparent name mangling" involves replacing characters in the address with equivalent HTML references from the list of XML and HTML character entity references.
- Posting all or part of the e-mail address as an image.
- Posting an e-mail address as a text logo and shrinking it to normal size using inline CSS.
- Posting an e-mail address with the order of characters jumbled and restoring the order using CSS.
- Building the link by client-side scripting.
- Using server-side scripting to run a contact form.
The use of images and scripts for address obfuscation can cause problems for people using screenreaders and users with disabilities.
According to a 2003 study by the Center for Democracy and Technology, even the simplest "transparent name mangling" of e-mail addresses can be effective.

More about End-user Anti-spam techniques (e-mail)...