Not really, according to the spec the '+' can be interpreted as part of the email address. The approach gmail takes seems to have gained widespread adoption, but it's not mandated by the spec.

Believe I saw this on HN recently: http://haacked.com/archive/2007/08/21/i-knew-how-to-validate...

I believe it is Gmail specific. Cursory search reveals that sendmail does that too, but I don't think it is specified in RFC. Feel free to correct me if I'm wrong.

It's more Sendmail and Exim and others did it, and Gmail does it too - not the other way around;)

With qmail the "standard"[1] was [email protected], rather than [email protected]. I rather prefer that - but then my (user)name(s) don't contain any hyphens.

Either way I think it looks better with system usernames - [email protected] was/is usually handled as a separate form of alias look-up anyway.

[1] http://www.lifewithqmail.org/lwq.html#dot-qmail-files See section "4.1.5. extension addresses"

[ed: and I recall using tmda as an anti-spam system - it inserts an encrypted tag in the alias portion, that can be stamped with an expiry date, and tied to a sender address (eg hmac(userkey, [email protected]+01012018) => xyxyzzzzz - give [email protected] the address [email protected] - and mail to that address will be accepted from only [email protected] until 1/1/2018.

http://tmda.sourceforge.net/cgi-bin/moin.cgi/AboutTmda ]

I don't have a source to a RFC, but all email's I've ever used let me do this. Including multiple different hosting services with my own domains, and my current work which is MS Exchange.