Anti-spam programs use a combination of methods to decide whether an email is likely to be spam. They can:
- Block email that comes from computers on a block list. This can be a commercially available list or a local list of computer addresses that have sent spam to your organization before.
- Block email that includes certain web addresses.
- Check whether email comes from a genuine domain name or web address. Spammers often use fake addresses to try to avoid anti-spam programs.
- Look for keywords or phrases that occur in spam (e.g., “credit card,” “lose weight”).
- Look for patterns that suggest the email’s sender is trying to disguise his or her words (e.g., “hardc*re p0rn”).
- Look for unnecessary HTML code (the code used for writing webpages) within email, as spammers often use HTML to try to conceal their messages and confuse anti-spam programs.
- Combine all the information it finds to decide the probability of an email being spam. If the probability is high enough, it can block the email or delete it, depending on the settings you choose.
Anti-spam software needs frequent updating with new rules so it can recognize the latest techniques used by spammers.
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