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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