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On PHP, running checkdnsrr('example.com.com', 'MX') returns 1 - I had expected it to return '0'. Replace 'example' with anything, and you get the same result.

Does that mean that cnet (who apparently own the com.com domain) receive any emails sent to somebody@example.com.com?

I'm interested because I am validating emails, and this has come up as a bug during the validation process.

This question has some useful information that seems to be relevant here: Using MX records to validate email addresses

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Dan Blows
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2 Answers2

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I believe example.org is setup for "testing", rather than example.com.com - that's the same as using anyone elses domain for testing.

Sparx
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    example.com and example.org are free to use for documentation purposes, but if your DNS server does not cache failures I'm not sure doing load testing against their (existing) DNS would be appreciated :) http://www.iana.org/domains/example/ – Joachim Isaksson Feb 17 '12 at 12:12
  • @Sparx you can replace 'example' with anything and you get the same result. In other words, *.com.com returns true when checking for an MX record. – Dan Blows Feb 17 '12 at 12:18
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I'm interested because I am validating emails, and this has come up as a bug during the validation process.

Such an excellent example makes perfectly clear that the very idea of validating emails by whatever action other than actual sending a letter to given address is utterly wrong.

Your Common Sense
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