Milter-greylist

Tere.
>
> However, you would never want to block them outright, since they're
> not known spammers (yet).  By delaying their mail, you give the
> blacklists time to receive reports, and then Spamassassin can kill
> them when it checks those blacklists.
>
>   
How many legal email have You received from these not know spammers yet? 
I presume none. Usually, if they appear in blacklist, their 
administrator tries soon to release from there. It can take less time 
then greylisting them in Your server.

-- 
Mart