[dns-operations] Curious use of cname

Mark Andrews marka at isc.org
Sun Aug 10 08:48:12 UTC 2014

In message <1407643575.596084963 at f209.i.mail.ru>, =?UTF-8?B?WW9uZ2h1YSBQZW5n?= 
>  Hi,
> @mail.china.com does provide free email service, and they have a large 
> number of user base.
> And their MX setup:
> mail.china.com. 297 IN CNAME mail.china.com.cachecn.com.
> mail.china.com.cachecn.com. 97 IN MX 10 mx-mail-china-com.icoremail.net.
> Will some email deliver systems break due to this setup? Thanks.

MTA's that follow RCF 822 will rewrite user at mail.china.com as
user at mail.china.com.cachecn.com.

MTA's that follow RFC 2822 or RFC 5322 won't preform the rewrite.

The better solution for this would be two MX records.

   mail.china.com. IN MX 10 mx-mail-china-com.icoremail.net.
   mail.china.com.cachecn.com. IN MX 10 mx-mail-china-com.icoremail.net.

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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