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We are trying to move all our websites we host to CNAMES as we are planning on moving servers in the new year and would like the ability to move some clients to one server and other clients somewhere else. We were planning on giving clients a unique CNAME which we can then change at a later date. (We have other reasons for doing this now but that is the main one)

We have been testing out this theory with a few of our own domains and it seemed to be fine. However when checking the MX records on a domain I got the CNAME value back rather than the MX record.

Sadly all of these domains are done via control panels, but I am guessing they are just writing zone files for me.

I want to create 2 CNAMEs for the company.com

company.com. IN CNAME client.dns.ourserver.com
www          IN CNAME client.dns.ourserver.com

The MX record is something like the following:

company.com  IN MX 10 mail.company.com

We have an A record for mail.company.com

Doing:

host -t mx company.com

Returns the CNAME value rather than the mx record.

Is this expected behaviour?

I have managed to get the above configuration working with the 123-reg.co.uk control panel, but not sure if that is more luck than anything.

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This is a common question and has been asked many times before. See this link for an example: serverfault.com/questions/18000/… –  Russell Heilling Dec 7 '09 at 16:11
    
I did spend a little while looking for an answer but couldn't figure out if I was doing something different. Especially as it is working fine with one domain provider. I have my answer so that is cool and hopefully it will be of some use to someone. –  johnwards Dec 7 '09 at 18:02
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2 Answers

up vote 15 down vote accepted

This is a common error. You cannot use a CNAME RR for your root domain (e.g. company.com) and define additional resource records for the same zone.

See Why can't I create a CNAME record for the root record? and RFC1034 section 3.6.2 for details:

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.

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You can use a CNAME on the root of the domain, however, those MX records must also be configured on the host record, so if you have mx1.mail.com configured on the zone for yourdomain.com, and the root of yourdomain.com is CNAME to thisrecord.cname.com, you must also make sure that mx1.mail.com is configured on that CNAME host; if not, all mail will be lost!

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The problem is, as per RFC1034, "if a CNAME RR is present at a node, no other data should be present" -- since the root needs to have NS records (to be useful, anyways), there will always be other data, which violates this section of the RFC. –  Doktor J Sep 30 '13 at 23:05
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