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Say you own a abcd.com and you only want to use it to send and receive email via bob@abcd.com. You don't want to provide any kind of website.

Can you set up the DNS records to include an "MX" record and no "A" record?

  • Is this enough for sending and receiving email to work?

  • Is this valid in terms of whatever standard defines these things?


Edit: To clarify, the mail server (terminology?) would not be hosted on abcd.com or *.abcd.com

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3 Answers 3

up vote 19 down vote accepted

As long as the system pointed at by the MX record has an A record itself, then yes.

For example: example.com can have a MX record pointing at mail.otherdomain.com. As long as the name mail.otherdomain.com itself is resolvable to an IP address, this is a valid configuration for example.com.

Strictly speaking, mail.otherdomain.com should be an A record with the IP address in order to be RFC-compliant. But this A record will be in the otherdomain.com domain, not in example.com.

Addressing your example, in order for bob@example.com to be a valid email address, mail.otherdomain.com needs to be configured to handle inbound mail for bob@example.com.

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1  
mail.otherdomian.com MUST be resolvable by A record so this answer is incorrect –  Jim B Jan 6 '10 at 15:39
2  
The mail-only domain does not require an A record if the MX record points to an A record in another domain. The question is only about the mail-only domain. –  Ben Doom Jan 6 '10 at 15:53
    
mail.otherdomain.com will have an A record in the otherdomain.com domain, not in the example.com domain. –  David Mackintosh Jan 6 '10 at 16:53

NO. The MX record points to a name. The names must be resolvable (via A record). The MX record should never point to a CNAME (RFC 1034 section 3.6.2, RFC 1912 section 2.4)

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True an MX records must point to an A record, but it doesn't have to point to one on the same domain. You could have the MX record for example.com pointing to mail.domain.com –  Sam Jan 6 '10 at 15:08
    
that's not the question- mail.domain.com MUST have an A record. It's required both by RFC and by definition –  Jim B Jan 6 '10 at 15:38
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Jim -- The question does not specity that the mx record point to the parent domeain. For example, I could point bendoom.com's MX record to Google mail, and have no A records in bendoom.com –  Ben Doom Jan 6 '10 at 15:52
    
Yes, mail.domain.com must have an A record, however he asked whether he needed an A record in abcd.com, if the MX record for abcd.com is pointing to mail.domain.com (or google.com etc) then he does not need an A record in the abcd.com DNS Zone –  Sam Jan 6 '10 at 15:57
    
You are correct, that's what the clarification says NOW but not when I answered the question. There was no mention of another domain. It then goes on to what the standard says. In addition being resolvable does not mean it's a A record. That being said, most mail servers will still submit mail to a CNAME; however, you can't be guaranteed of it. –  Jim B Jan 6 '10 at 16:45

It is possible - if mail over IPv6 ONLY is desired - as the AAAA record pointed at by the MX record satisfies the address target requirement. Granted, IPv4-only hosts won't be able to contact such a setup, but that doesn't make it illegal under DNS rules.

Why were all the prior answers so IPv4-centric?

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