Milter-greylist

>> senderbase is meant to be more like "scoring" system ranking the
>> sender's IP from -10 (a spammer) to 10 (innocent guy) -> so I
>> thought we could use it for whitelisting as well.
> 
> We certainly can.  In fact, it would probably only take a small
> tweak to my script to do that; offer a different URL and create a
> different link and you're done.  That's a really good idea,
> actually.  I'll implement it when I have a spare moment.

I changed my mind.  Senderbase is an index of reported or otherwise
collected spam.  They do not have reliable numbers for non-spam email.

If you click on the [SB] link at the bottom end of the "spam reports
vs email volume" chart, you'll see that every IP in that block is
listed in 2-3 RBLs.  Using the opposite end of chart I pull my data
from, you can see there is almost no data, and one of the three IPs is
listed in two RBLs.  I see no useful data in any configuration here.

Best to stick with DNSWL.  Maybe also use some other whitelists too,
but be careful; some whitelists are rather generous (ASPATH and RDNS
simply verify real live servers rather than trustworthiness.  See
http://openrbl.org/client/#213.144.132.251 (good entry) versus
http://openrbl.org/client/#212.76.37.150 (bad entry) and click on the
hits' corresponding wiki pages.

I won't use whitelisting services that charge entrants for listing
based on the simple principle that it's akin to extortion: "pay us for
whitelisting or your mail won't get through!"