Does an email address domain require a dot?

Question

I noticed that when constructing instances of the System.Net.Mail.MailAddress class, it does not throw an exception for the email string foo@bar. This surprised me a bit since I don't recall seeing emails where the domain does not have a . in it. Is the domain bar really valid email address syntax?

Answer 1

There’s nothing stopping TLD registry operators serving a records at the apexes of their TLD zones. For example, if Verisign (the operator of the com TLD registry) wished, they could add an A record at the apex of the com TLD zone – com would then resolve to that IP, and your browser would connect to that IP when you visited https://com.

Does any registry operator actually do this though? Surprisingly, the answer is yes.

• http://ai is a nice retro landing page for “Offshore Information Services”, who seem to maintain the .ai TLD
• http://pn serves an “it works” page; https://pn serves “hello world” (with an invalid certificate)
• http://uz serves a HTTP 500; https://uz serves the Uzbekistan ccTLD’s homepage (with an invalid certificate)
• http://мон eventually serves a blank page, but does also serve a favicon; https://мон eventually serves a default Apache landing page (with an invalid certificate)

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