[Mimedefang] variables available for greylisting

[kamal]

> Could I be so lucky as to simply set "MX_RECIPIENT_CHECK=no" in
> /etc/sysconfig/mimedefang (to disable filter_recipient), and then rename my
> filter)recipient to something like "sub my_greylist" and expect it to work?

Yes, but that's half of the story. Then you have to call my_greylist 
with proper arguments and check its return status and do something. 
Better change the return values in my_greylist to something simpler. 
You'll have to call it for each recipient and decide whether to tempfail 
or accept, in either case for *all* recipients.
The arguments can be ($Recipients[index], $Sender, $RelayAddr)