http://drjtumblr.disqus.com/Dr J's TumblrenWed, 04 Mar 2009 13:56:34 -0000http://tumblr.craigjolicoeur.com/post/83461841#comment-6876909<p>This remains one of my biggest usability pet peeves!</p>WinfieldWed, 04 Mar 2009 13:56:34 -0000http://tumblr.craigjolicoeur.com/post/83461841#comment-6870826<p>Back in the day, you couldn't just claim something on the Internet was valid without quotin' an RFC. These days Wikipedia is the shortcut:</p><p><a href="http://en.wikipedia.org/wiki/E-mail_address#Sub-addressing" rel="nofollow noopener" target="_blank" title="http://en.wikipedia.org/wiki/E-mail_address#Sub-addressing">http://en.wikipedia.org/wik...</a></p><p>The problem with plus sub-addressing is that it's an MUA feature, and not functionally specified in RFC 5322, which defines email address formats. <a href="http://tools.ietf.org/html/rfc5322#section-3.2.3" rel="nofollow noopener" target="_blank" title="http://tools.ietf.org/html/rfc5322#section-3.2.3">RFC 5322 3.2.3</a> lists the following as valid characters for the local-part of an email address:</p><p><code><br> atext = ALPHA / DIGIT / ; Printable US-ASCII<br> "!" / "#" / ; characters not including<br> "$" / "%" / ; specials. Used for atoms.<br> "&amp;" / "'" /<br> "*" / "+" /<br> "-" / "/" /<br> "=" / "?" /<br> "^" / "_" /<br> "`" / "{" /<br> "|" / "}" /<br> "~"<br></code></p><p>The definition of sub-addressing is in <a href="http://tools.ietf.org/html/rfc5233" rel="nofollow noopener" target="_blank" title="http://tools.ietf.org/html/rfc5233">RFC 5233</a>, "Sieve Email Filtering: Subaddress Extension". That one's pretty obscure, and you always find 5322 if you go looking for the format definition. But of course web developers don't read RFCs, they just copy magickal regexp incantations that they find on the Google.</p>hybernautWed, 04 Mar 2009 10:18:19 -0000