[UA-EAI] Email address syntax

[Arnt Gulbrandsen]

Hi,

I promised to write something about email address syntax. It’s actually a touch more complicated than I mentioned yesterday. As John says, Email addresses are more complicated than one usually sees, and there exist syntax features that can be used to confuse people. But, I think, three reduced grammars:


  1.  One might say that banning all the obs- productions in RFC5322 produces a reduced grammar. Those productions are obsolete, that’s why they’re called obs-whatever, and should not be used. Noone uses them anyway, I’m only mentioning this for completeness.
  2.  The WHATWG HTML specification contains a simple grammar, which web browsers implement. Since one must expect email addresses to be typed into HTML forms, IMO following this specification is strongly advisable. The spec is on https://html.spec.whatwg.org/multipage/input.html#email-state-(type=email) and so far isn’t UA-ready. I fear that getting that UA-ready will shortly be one of my tasks.
  3.  \X+ is an extremely simple PCRE (a regular expression) that IMO should match all addresses. I suspect we’ll see that in some well-known web software in the near future.

IMO it’s safe to advise anyone to use only addresses that match the WHATWG spec (when extended) and also match \X+.

The two suggestions complement each other; “ “@example.com<mailto:“%20“@example.com> matches \X+ but I’m not brave enough to use that an address like that 😉

--
Arnt Gulbrandsen
UA Technology Sr. Manager, ICANN
+32 492 374706
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