The Evolution of Spam
Until a while ago, spam was the domain of text- or html-based emails. For anonymous delivery, these messages traditionally relied on abusing open SMTP relays. When open SMTP relays became less common, spammers switched to proxy servers, dial-up services and more recently, hijacked computers. Spammers designed personalized template emails to deliver their messages and then made use of bulk mailing software for distribution.
To block spam, email service providers and companies often relied on keyword ‘detection’, and drew up a list of keywords that commonly appeared in most of the spam email. This list would often include keywords such as ‘viagra’ or ‘bank’.
However, this method often blocked genuine email and adding more keywords simply resulted in more false positives which in turn blocked legitimate email. But spammers became smarter too, and they addressed keyword blocking by replacing keywords such as ‘viagra’ to ‘v1agra’.
Another attempt at blocking spam includes making use of blacklists that contain a list of IP addresses of known spammers or compromised hosts.
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