Server Fault is a question and answer site for system and network administrators. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Somebody has 2 e-mail addresses: and . The DNS records for these domains look like this:

$ dig any
;; ANSWER SECTION:  86179   IN  SOA 2010081200 20000 4000 1409600 86400  86179   IN  MX  10  86179   IN  A   177.39.XXX.YY  85342   IN  NS


;; ADDITIONAL SECTION:  86179   IN  A   177.39.XXX.YY  85342   IN  A   177.39.XXX.YY

$ dig any
;; ANSWER SECTION: 37036   IN  SOA 1229685618 10800 3600 604800 38400 37036   IN  A   177.39.XXX.YY 37036   IN  NS


;; ADDITIONAL SECTION:  85036   IN  A   177.39.XXX.YY

The doesn't have a MX record. However, when I send an e-mail to, it gets delivered, and the receiver reply using the address. The e-mail sent to is probably being redirected to How is this possible, given that doesn't have a MX record?

share|improve this question
up vote 46 down vote accepted

According to the Section 5 of RFC 5321, if no MX record is present mail servers should fall back to the A record for the domain. This is probably what's happening.

share|improve this answer
And since the A record for both domains appear to resolve to the same IP address (despite the obfuscation) my guess is that there's an SMTP server at that ip address that accepts emails for both domains and deilvers them to a mailbox for – joeqwerty Jan 19 '13 at 17:27

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.