I'm with you. I came across a mail server which was (reportedly) checking the rDNS for the IP corresponding to the A record which the MX pointed to. This was an entirely different host than the one sending the message. I realize MX is only used for incoming messages, and thought it was a rather pointless check. Perhaps it was a misconfigured email gateway of some sort.
I just wondered if it might be a legitimate thing to check. It's sort of like saying "I'm going to check your incoming configuration for errors before I accept a message from your domain". Rather pointless in some senses. In any case, to implement this, spamdyke would do an rDNS check on the IP address corresponding to each MX name, and also check to be sure the rDNS name resolves. It would be (one or) two additional DNS lookups per MX, and would only make sense to do when "reject-missing-sender-mx" is in effect. It would be something like "reject-empty-sender-mx-rdns" and "reject-unresolvable-sender-mx-rdns". I just don't know if this check would be worthwhile or not. Definitely a low priority. Thanks Sam! -- -Eric 'shubes' On 10/03/2013 08:27 PM, Sam Clippinger wrote: > I'm not exactly sure what you're describing here. MX records are supposed to > be names, not IP addresses. spamdyke's "reject-missing-sender-mx" option > already checks for the existence of an MX record, then tries to resolve each > name to an IP address. I'm not sure I would see the point in trying to > resolve each IP address' reverse DNS name; reverse DNS is generally required > for IP addresses where email connections originate, not where they terminate. > In other words, outgoing servers should have valid rDNS, but incoming > servers aren't required to have it -- if a server is willing to accept email, > that's not necessarily an indication it's a spam source. > > Some DNS administrators mistakenly set their MX records to contain IP > addresses. This is technically illegal, but spamdyke honors them as valid > with no further checking. > > So anyway, I think I'm misunderstanding what you're asking for. :) > > -- Sam Clippinger > > > > > On Oct 3, 2013, at 7:16 PM, Eric Shubert wrote: > >> I don't know if this has come up before, but it just came to my >> attention that there are some mail servers which check rDNS of domain MX >> records before accepting emails. I don't believe spamdyke does this. >> >> Is this a total waste, or would it perhaps catch some spammers? >> >> Some domains have many MX records. I wonder if all MXs are checked, or >> only the highest priority? >> >> Seems like a bit of a waste of resources to me. Any thoughts about this? >> >> (I'd certainly prefer to see SPF implemented than MX rDNS checking!) >> >> Thanks Sam (and everyone). >> >> -- >> -Eric 'shubes' >> >> _______________________________________________ >> spamdyke-users mailing list >> [email protected] >> http://www.spamdyke.org/mailman/listinfo/spamdyke-users _______________________________________________ spamdyke-users mailing list [email protected] http://www.spamdyke.org/mailman/listinfo/spamdyke-users
