Greylisting is a new tool in the fight against spam. What it does is temporarily block incoming mail from a sender. It returns the mail to the sender’s mail server with a message saying try again later. The sending server must then retry sending the mail after the Block Period but before the Pass Period.
Greylisting [...]

SmarterMail uses multiple SPAM checks to determine the probability of SPAM. These include by are not limited to ‘Bayesian Filtering’, Greylisting, ‘ORDB 10 SPAM List’, ‘SPAMCop SPAM List’, ‘SPAMHaus SBL+XBL SPAM List’.
If the email fails one of the SPAM checks above, SmarterMail adds a SPAM Weight of 10 to the email. The total weight of [...]