anti-SPAM protection; content-base SPAM search; electronic mail; greylisting; SPAM control; SMTP

Current studies conducted by industry leading companies suggest that the SPAM ratio has been decreasing recently. However, the SPAM ratio obtained from the SMTP servers at two mid-scale universities does not confirm this tendency. The article describes a multilevel anti-SPAM mechanism and introduces possible improvement of the system by incorporating the feedback interconnection between its two key components (greylisting and content-based search). The estimation of the efficiency increase due to this improvement is presented as well.