Wednesday, 13 June 2012

New type of email address

I have wondered if I could have a shorter email address. Something like is pretty short, but what of say e@gg ?

My understanding is that the guy running gg actually tried it, and found it did not work. Partly down to email clients, but annoyingly, whilst a top level domain can have an MX record, it is actually part of the RFC that disallows this.

RFC2822 makes domain :-
 Domain = (sub-domain 1*("." sub-domain)) / address-literal

But the older RFC822 made it :-
 domain = sub-domain *("." sub-domain)

So it used to allow a domain with no dots in it, but now requires dots.

Shame, especially for many of those applying for new TLDs as they cannot have things like info@google as an email address.

Update: See comments as it seems I missed something and such email addresses are valid, just unlikely to work.


  1. Would it work if you just stuck a trailing period on the end, i.e. an 'empty' final domain?

    1. No, a trailing '.' is not permitted by the RFCs - see the ABNF definition above or check RFC5322 3.4.1.

  2. Not sure how you read the RFC, but RFC 5322 (and 2822 which it supersedes) both have:

    atext = ALPHA / DIGIT / ...
    dot-atom-text = 1*atext *("." 1*atext)
    dot-atom = [CFWS] dot-atom-text [CFWS]
    domain = dot-atom / domain-literal / obs-domain

    dot-atom-text isn't '1*atext 1*("." 1*atext)' in either.

    Note also that RFC5321 specifically mentions this case:

    2.3.5. Domain Names

    A domain name (or often just a "domain") consists of one or more
    components, separated by dots if more than one appears. In the case
    of a top-level domain used by itself in an email address, a single
    string is used without any dots.

    I think it's more likely that MTAs tend to rewrite unqualified addresses into their own domain, or assume they are a local host. No '.' definitely looks far more like a hostname than a FQDN. It was common practise a few years ago to assume no '.' meant a local hostname, but these days seems to have fallen out of use a bit, both with centralised e-mail systems and as people make so much use of address books as they have so many contacts. Shortening addresses is just not needed so much.

    It's also a consequence of the spam battle - localpart@hostname is so uncommon, and occurs in spam, so it's likely to get blocked.

    The biggest problem is probably web page e-mail address verifiers. Most of them are horribly broken, and assume something much simpler than the RFCs actually allow (spaces in a local part, for instance - there's nothing syntactically wrong with "The Reverend"@gg, or even !@gg).

    So although it sounds like a nice idea for a short address, it's likely to have so many issues you'd be unable to use it most of the time.

    1. Very comprehensive reply, thanks. I obviously missed something there... I was copy/pasting from the RFCs.