 <p>The HTML5 spec has an <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/states-of-the-type-attribute.html#valid-e-mail-address" rel="nofollow noreferrer">interesting take on the issue of valid email addresses</a>:</p> <blockquote> <p>A valid e-mail address is a string that matches the ABNF production 1*( atext / "." ) "@" ldh-str 1*( "." ldh-str ) where atext is defined in RFC 5322 section 3.2.3, and ldh-str is defined in RFC 1034 section 3.5.</p> </blockquote> <p>The nice thing about this, of course, is that you can then take a look at the open source browser's <a href="https://bug555559.bugzilla.mozilla.org/attachment.cgi?id=461895" rel="nofollow noreferrer">source code for validating it</a> (look for the <code>IsValidEmailAddress</code> function). Of course it's in C, but not too hard to translate to JS.</p>