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
