I've been working with a client running Exim on a cheap shared host who has been having some odd delivery issues. Normally I don't get too involved in these, but it was interesting. It only affects some recipients some of the time and the only reason I can find for the inconstancy is what appears to be a bit of a hooky DNS set up.
Can someone just give me a logic check here? The host concerned has a PTR record, it's a bit of a mess, but it's there: dig -x 205.134.224.208 208.224.134.205.in-addr.arpa. 17019 IN CNAME 208.128-255.224.134.205.in-addr.arpa. 208.128-255.224.134.205.in-addr.arpa. 65020 IN PTR whub28.webhostinghub.com. So this basically gives back hostname: whub28.webhostinghub.com. However, digging this gives two A records/IP's back rotating on a round robin: dig +short whub28.webhostinghub.com. 205.134.241.17 205.134.224.208 dig +short whub28.webhostinghub.com. 205.134.224.208 205.134.241.17 dig +short whub28.webhostinghub.com. 205.134.241.17 205.134.224.208 I think this may be a problem with PTR resolution because if the reverse lookup for a connecting IP gives the name whub28.webhostinghub.com, but the matching double check on that back to an IP gives two records back will the average mail resolver see both of these and satisfy the check, or will it take the top one only and spot the mismatch between the original connecting IP and the RrDNS? Basically, is this OK or is it sub optimal/likely to break any RFC's? To me it looks like a cheap attempt at load balancing / redundancy in DNS - but it is probably perfectly legal, even if it may break RrDNS for some receiving mail engines. Any input, reasoning greatly appreciated. Warm regards Ron -- ## List details at https://lists.exim.org/mailman/listinfo/exim-users ## Exim details at http://www.exim.org/ ## Please use the Wiki with this list - http://wiki.exim.org/
