CNAME for MX Record?
Mark Andrews
marka at isc.org
Wed Aug 19 23:26:38 UTC 2009
In message <84010000908190935r6f7d622am9dd697317ec5a6a at mail.gmail.com>, Bradley
Caricofe writes:
> 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=
> E:
>
> [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=
> .typepad.com.
>
> ;; 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?
>
> Thanks,
> Brad
> _______________________________________________
> bind-users mailing list
> bind-users at lists.isc.org
> https://lists.isc.org/mailman/listinfo/bind-users
The nameservers for meetingtoolsandjewels.com
(ns[1234].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
meetingtoolsandjewels.com.
named enforces this restriction. Unfortunately other vendors
don't which leads to these sorts of operational problems.
RFC 1034
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 64.94.117.199
ns2.nameresolve.com. 86400 IN A 63.251.83.88
ns3.nameresolve.com. 86400 IN A 66.150.161.151
ns4.nameresolve.com. 86400 IN A 64.94.31.66
;; Query time: 193 msec
;; SERVER: 64.94.117.199#53(64.94.117.199)
;; WHEN: Thu Aug 20 09:26:14 2009
;; MSG SIZE rcvd: 252
Mark
--
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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