On Fri, 23 Aug 2013, keld wrote:
Thi idea was to use it as a check in addition to DNSBL etc.
The advantage over DNSBL is that for DNSBL you first need to register
the offending site with DNSBL.
Not necessarily. See for instance http://www.spamhaus.org/pbl/
FWIW, I just checked the sending IP addresses a bunch of spam emails that
weren't listed at Spamhaus ZEN at time of delivery. A significant minority
of them (~ 40%) was listening on port 25.
At the same time, several IP addresses that were sending legitimate email
weren't.
Perhaps, if you do it very carefully, adding a tiny score for emails
delivered from an IP address that wasn't listening on port 25 will improve
your filter's performance by 0.03%.
Or perhaps it won't.
Martijn.
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