In my SA stats, the majority (+90%) of email inbound is classified as rdns_none.
I have a suspicion that this is due to the IPv6-IPv4 mapped address being written into the headers when I am speaking to a non-native IPv6 MTA: Received: from unknown (HELO mail.apache.org) (::ffff:140.211.11.2) by pearl.ibctech.ca with SMTP; 28 May 2008 09:13:00 -0000 (I presume you are trying to make this server IPv6 only instead of dual stack. When my machine had a globally routable v6 address I got some mail over v6 and some over v4, but didn't used mapped addresses.) It seems that your SMTP listener is not correctly doing reverse dns lookups of mapped addresses, and I'm not sure what the right fix is. Either the SMTP code should notice the mapped address, pull out the v4 address, and look it up, or the resolver should do this automatically. On my NetBSD 4 system (generally pretty hard core about this sort of thing), "dig -x ::ffff:140.211.11.2" returns NXDOMAIN on a query of ;2.0.b.0.3.d.c.8.f.f.f.f.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa. IN PTR so I'd guess that it's not a normal expectation for a resolver to extract the mapped address. After the lookup issue is fixed, the received header would have the hostname. >From looking at Received.pm, I don't see that SA is trying to do DNS lookups; rnds_none seems to be about the MTA not having succeeded at rdns lookup, not SA checking it later. But if SA does look it up, teaching it about mapped addresses might be needed too.
