[Mimedefang] Domain canonifyin​g and RFCs

Kees Theunissen theuniss at rijnh.nl
Wed Oct 19 16:42:12 EDT 2011

On Thu, 13 Oct 2011, Ernst du Plooy wrote:

>They insist their DNS settings are RFC compliant.
>Their DNS records looks like this:
>c.domain.com      IN      A
>a.b.domain.com.  IN      CNAME   c.domain.com.
>c.domain.com.    IN      MX      10   mail.domain2.com
>c.domain.com.    IN      MX      20   mail2.domain2.com
>user at a.b.domain.com will be rewitten to user at c.domain.com

Yes, their DNS settings are RFC compliant.

But IMHO they should realize that:
1) This construction was not RFC compliant in the past and there has
   been -in the past- a long tradition of rewriting such addresses.
2) The past never ends.
3) They cannot control how third parties handle their addresses.
   (I don't assume that you are the only third party involved in using
   those addresses.)
So they better should be prepared to handle inbound mail directed to the
rewritten adresses if they insist on using this CNAME. Or they should
accept losing some mail.

Notwithstanding the above, you probably shouldn't rewrite those

Best regards,


Kees Theunissen
F.O.M.-Institute for Plasma Physics Rijnhuizen, Nieuwegein, Netherlands
E-mail: theuniss at rijnh.nl,  Tel: (+31|0)306096724,  Fax: (+31|0)306031204

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