Experts say the best way to deal with the constant barrage of unwanted commercial e-mail, or spam, is to <A HREF="http://searchdomino.techtarget.com/originalContent/0,289142,sid4_gci960396,00.html"></A>et up several layers of defense at various points in your company's messaging infrastructure. Conventional thinking holds that the most effective way to avoid spam is to examine the body and subject line of incoming messages with e-mail filtering programs that employ Bayesian logic, which uses knowledge of past behavior to decide which e-mails to accept.