Why has the spam volume been increasing for companies?
The dramatic growth of spam has been fueled by the use of a sophisticated email address collection technique called a Directory Harvest Attack (DHA). Spammers use DHAs to collect thousands of valid email addresses from unprotected mail servers. They also have become more advanced in the use of graphics, HTML, and techniques that introduce minor differences into each spam message. This technique is used to defeat the simple signature-based or reference database anti-spam methodologies (that depend upon large volumes of identical message being sent in order to identify junk email). Postini’s experience is that 90% of spam messages are unique — so these types of filtering technologies are often ineffective.
