CNAME for MX Record?
marka at isc.org
Wed Aug 19 23:26:38 UTC 2009
In message <84010000908190935r6f7d622am9dd697317ec5a6a at mail.gmail.com>, Bradley
> Hey list,
> I have the following issue. A customer hosts a domain with me,
> facplus.com. Her primary email account is on that domain, we'll call
> it her at facplus.com. She has also registered another name through
> Dotster, meetingtoolsandjewels.com. Dotster provides her with URL
> redirection and email forwarding for that domain. She has setup an
> email address, we'll call it her at meetingtoolsandjewels.com, which
> should forward to her at facplus.com.
> We've been having a problem where not all senders are being received
> when mail is sent to the her at meetingtoolsandjewels.com account. I've
> sent her test emails from gmail, yahoo and my own server (sendmail)
> and all were received. When I send emails from systems using exchange,
> I eventually get a bounce that the message has been delayed...it's
> never received.
> When I do digs for the MX record for meetingtoolsandjewels.com I get a CNAM=
> [root at jump1 ~]# dig meetingtoolsandjewels.com MX
> ; <<>> DiG 9.3.4-P1 <<>> meetingtoolsandjewels.com MX
> ;; global options:=A0 printcmd
> ;; Got answer:
> ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 5373
> ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 0
> ;; QUESTION SECTION:
> ;meetingtoolsandjewels.com.=A0=A0=A0=A0 IN=A0=A0=A0=A0=A0 MX
> ;; ANSWER SECTION:
> meetingtoolsandjewels.com. 3600 IN=A0=A0=A0=A0=A0 CNAME=A0=A0 meetingsmaven=
> ;; AUTHORITY SECTION:
> typepad.com.=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 600=A0=A0=A0=A0 IN=A0=A0=A0=
> =A0=A0 SOA=A0=A0=A0=A0 ns1.sixapart.com.
> hostmaster.sixapart.com. 2009051400 10800 3600 604800 600
> ;; Query time: 233 msec
> ;; SERVER: 192.168.75.1#53(192.168.75.1)
> ;; WHEN: Wed Aug 19 04:44:21 2009
> ;; MSG SIZE=A0 rcvd: 139
> If I do digs against her actual nameservers, I get a correct MX
> record. What the heck am I seeing here and is this the likely cause of
> the delayed emails?
> bind-users mailing list
> bind-users at lists.isc.org
The nameservers for meetingtoolsandjewels.com
(ns.nameresolve.com) don't enforce the CNAME and no
other data restriction from RFC 1034. This leads to
inconsistant results depending apon what data is in the
cache as there are both a MX and CNAME records at
named enforces this restriction. Unfortunately other vendors
don't which leads to these sorts of operational problems.
The domain system provides such a feature using the canonical name
(CNAME) RR. A CNAME RR identifies its owner name as an alias, and
specifies the corresponding canonical name in the RDATA section of the
RR. If a CNAME RR is present at a node, no other data should be
present; this ensures that the data for a canonical name and its aliases
cannot be different. This rule also insures that a cached CNAME can be
used without checking with an authoritative server for other RR types.
; <<>> DiG 9.3.6-P1 <<>> mx meetingtoolsandjewels.com @ns1.nameresolve.com
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 5920
;; flags: qr aa rd; QUERY: 1, ANSWER: 2, AUTHORITY: 4, ADDITIONAL: 4
;; QUESTION SECTION:
;meetingtoolsandjewels.com. IN MX
;; ANSWER SECTION:
meetingtoolsandjewels.com. 1800 IN MX 0 m1.dnsix.com.
meetingtoolsandjewels.com. 3600 IN CNAME meetingsmaven.typepad.com.
;; AUTHORITY SECTION:
meetingtoolsandjewels.com. 86400 IN NS ns1.nameresolve.com.
meetingtoolsandjewels.com. 86400 IN NS ns2.nameresolve.com.
meetingtoolsandjewels.com. 86400 IN NS ns3.nameresolve.com.
meetingtoolsandjewels.com. 86400 IN NS ns4.nameresolve.com.
;; ADDITIONAL SECTION:
ns1.nameresolve.com. 86400 IN A 188.8.131.52
ns2.nameresolve.com. 86400 IN A 184.108.40.206
ns3.nameresolve.com. 86400 IN A 220.127.116.11
ns4.nameresolve.com. 86400 IN A 18.104.22.168
;; Query time: 193 msec
;; SERVER: 22.214.171.124#53(126.96.36.199)
;; WHEN: Thu Aug 20 09:26:14 2009
;; MSG SIZE rcvd: 252
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742 INTERNET: marka at isc.org
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