On 5/5/2013 8:10 PM, Vincent Lefevre wrote: > On 2013-05-02 11:08:13 -0500, Noel Jones wrote: >> If the DNS lookup fails with a temporary error, the mail will be >> deferred. >> >> It's important to note that not all clients labeled as "unknown" >> will be rejected by reject_unknown_reverse_client_hostname. >> >> For enlightenment, compare the docs on >> reject_unknown_client_hostname (a strict test not widely used), with >> the docs on reject_unknown_reverse_client_hostname (a generally safe >> check). > [...] > > In order to be sure, I decided to check against my mail archive. > I've written a small Perl script for that (attached). Some clients > don't seem to have a reverse hostname. Both IPv4 and IPv6 are > concerned. For instance: > > Received: from carotte.tilapin.org (unknown [95.138.72.61]) > by ioooi.vinc17.net (Postfix) with ESMTPS id EFA4959 > for <vinc...@vinc17.net>; Tue, 2 Oct 2012 03:15:23 +0200 (CEST) > > $ host 95.138.72.61 > Host 61.72.138.95.in-addr.arpa. not found: 3(NXDOMAIN)
Most large mail providers outright reject mail from such clients. The few that don't reject it send it straight to the spam folder. That doesn't mean there are no clients without valid rDNS. You'll just be one more of the many they have trouble with. > > and this is from a Debian developer. > > There's something that is quite strange with one of the mail I've > sent from my machine at work (ypig): > > Received: from ypig.lip.ens-lyon.fr (unknown > [IPv6:2002:8c4d:d7f:1:21f:29ff:fe04:3efb]) > by ioooi.vinc17.net (Postfix) with ESMTPS id A053EA4 > for <vincent-h...@vinc17.net>; Tue, 12 Feb 2013 14:12:33 +0100 (CET) > > An IPv6 address is listed while it was an IPv4 connection (IPv6 > doesn't work at ens-lyon.fr as shown by "ping6" and "ssh -6" from > ypig to ioooi, which give a "Network is unreachable" error). It > seems to be the only exception for this machine (the IPv4 address > with the associated reverse hostname is normally given). Is there > any explanation? > > Note: for this date, I no longer have any logs. > Postfix logs what the system reports to it. Apparently IPv6 worked at some point with this particular client. -- Noel Jones
