What is the actual minimum length of an email address as defined by the IETF?

Question

I'm specifically looking for the minimum length of the prefix and domain.

I've seen conflicting information and nothing that looks authoritative.

For reference, I found this page which claims that a one character email address is functional:

http://www.cjvandyk.com/blog/Lists/Posts/Post.aspx?ID=176

I tried validating email addresses at Gmail and they expect prefix greater than or equal to 6.

These are obviously way off.

My web framework expects prefix greater than or equal to 2.

Solution 1

well the problem is really the question.. email depends on if it is sent over the internet, or within a closed system (eg intranet). over the internet, I believe [email protected] is the shortest email possible (e.g. google's G.CN for china would result in the shortest email adress possible, e.g. [email protected], which is 6 characters long). on the intranet however, it is an entirely different thing, and i@y would be possible, which is just 3 characters long.

Solution 2

I believe the standard you are looking for is RFC 2822 - Internet Message Format

More specific info on email address restrictions in RFC 3696 - Section 3

To quote the spec:

Contemporary email addresses consist of a "local part" separated from a "domain part" (a fully-qualified domain name) by an at-sign ("@").

So three characters is the shortest.

I originally got this info from Phil Haack's blog post.

Solution 3

Many mail-servers will not accept the email-address if there aren't at least 2 characters before the @. That doesn't make it an invalid address, but if the servers don't know that, it sure can lead to a lot of problems.

Comments

[ZygD]

Where does this say minimum length?

[Josh Stodola]

It's in there. Not only is one character valid, but it doesn't have to be alpha-numeric!

[Josh Stodola]

I agree. Most standards are.

[David Watson]

Is this claiming that the shortest valid email address is 3 characters (a@b) or 1 character?

[Josh Stodola]

@David To quote the spec Contemporary email addresses consist of a "local part" separated from a "domain part" (a fully-qualified domain name) by an at-sign ("@"). So three characters is the shortest.

[kaleissin]

You can set up an MX or A to answer for a top-level domain, so that you could have somealias@com. I believe that's been done. You can set up a new top-level domain on your own name server only visible to machines you control, and thus make a one-letter top-level domain, for a minimum of 3 letters including the '@'.

[Janus Troelsen]

It doesn't say the local part can't be 0 characters.

[Pedro Emilio Borrego Rached]

given this i think the proper answer for a valid "internet" email address will be a minimum length of 4 (including . and @), and for an intranet a minimum length of 3 including the point.

[Matt Welke]

Glad I found this. I'm testing out a new email regex to use in an open source validation library and our current test suite fails with the new regex with [email protected] but passes with [email protected], so it seems like this new Regex I obtained asserts that the local part must be two characters long. I can't seem to find out why, but it must be this. It's probably best to enforce this minimum length then.