Greylisting never permits from=<>

Philip Hachey
Wed Nov 9 15:40:38 UTC 2005

I've discovered a problem with dccm greylisting: messages with env_from's 
of <> (which are completely valid -- return receipts, etc.) are never 
learned and perpetually embargoed.  Ideally, this would be handled by dccm 
and dccd as a triple (env_from=NULL,env_to=<receiver's 
address>,relay=<sender IP>) but, apparently, this doesn't happen.  To work 
around this, I put in my grey_whitelist the line "ok   env_from   <>", but 
this obviously opens an easily exploited hole in greylisting as even never 
before seen sender IP addresses would get through if the env_from is null 
-- a common practice by spammers.

Philip J. Hachey, BCS(High Hons)
City of Cornwall

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