How well does Stack Overflow's own e-mail validation regex work?

Question

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What is the best regular expression for validating email addresses?

I found this e-mail validation regular expression in Stack Overflow's own answer page code. Is it valid/effective?

function saveEmailNotification(email) {
    // only post if the email is valid
    if (!(/^[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}$/i).test(email)) return;
...
}

it passed basic validation ! But as i'm not able to read regex i dont know what the code actually means :( — Sourav, May 20 '11 at 16:07
related: http://stackoverflow.com/questions/1903356/email-validation-regular-expression/1903368#1903368 — Matt, May 20 '11 at 16:07
@Sourav, do you think I do? I can't read regex, as I'm human. — Blender, May 20 '11 at 16:09
@Sourav: No, it's not a good one; this is several kinds of broken. info@example.भारत might be a valid e-mail address, yet it fails your test. What it does is takes valid e-mail addresses and rejects them; you shouldn't use it. — Piskvor left the building, May 20 '11 at 16:12
@Sourav: This is SO code?!? o_O I'm shocked, *shocked*! I will be asking the same question. — Piskvor left the building, May 20 '11 at 16:21
@Piskvor Yup, in a function called `function saveEmailNotification` , and thats the reason i asked here, people are closing the question :( HELP !!! — Sourav, May 20 '11 at 16:23
It looks like this function is actually not used when setting email notifications, but is indeed hanging there in the source code. — pimvdb, May 20 '11 at 16:51
See me rant, all righteously indignant and foaming at the mouth, in the "Letters to editor" section: http://meta.stackexchange.com/questions/92094/false-negatives-when-validating-notification-e-mails-widespread-sloppy-coding-e (in other words, I added this as a bug on Meta) — Piskvor left the building, May 20 '11 at 18:39
Update: It is being used (check by tracking XHR requests in Chrome Dev Tools). — pimvdb, May 20 '11 at 19:42

score 3 · Accepted Answer · answered May 20 '11 at 16:26

No need to re-invent the wheel. From jQuery validation (see http://bassistance.de/jquery-plugins/jquery-plugin-validation/):

function validateEmail(value){return /^((([a-z]|\d|[!#\$%&'\*\+\-\/=\?\^_`{\|}~]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])+(\.([a-z]|\d|[!#\$%&'\*\+\-\/=\?\^_`{\|}~]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])+)*)|((\x22)((((\x20|\x09)*(\x0d\x0a))?(\x20|\x09)+)?(([\x01-\x08\x0b\x0c\x0e-\x1f\x7f]|\x21|[\x23-\x5b]|[\x5d-\x7e]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(\\([\x01-\x09\x0b\x0c\x0d-\x7f]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF]))))*(((\x20|\x09)*(\x0d\x0a))?(\x20|\x09)+)?(\x22)))@((([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])([a-z]|\d|-|\.|_|~|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])*([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])))\.)+(([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])([a-z]|\d|-|\.|_|~|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])*([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])))\.?$/i.test(value);}

score 2 · Answer 2 · answered May 20 '11 at 16:09

2

/^[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}$/i

^ means start of the string

[A-Z0-9._%+-]+ means: one or more of these characters

@ means a @ should come now

[A-Z0-9.-]+ means: one or more of these characters

\. means a . should come now

[A-Z]{2,4} means: 2, 3 or 4 letters

$ means end of string

i is a flag indicating it accepts both lowercase and uppercase.

answered May 20 '11 at 16:09

pimvdb

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@Sourav: yes, they do; plus they support various other characters like `[{}]` etc. – Piskvor left the building May 20 '11 at 16:15
google,yahoo still says `Only letters, numbers, underscores, and one dot (.) are allowed` – Sourav May 20 '11 at 16:17
@Sourav: ...when choosing your username __at those providers__. Google isn't the whole world (yet ;)). – Piskvor left the building May 20 '11 at 16:23
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Google, hotmail, yahoo, rediff i think the list is complete :P – Sourav May 20 '11 at 16:24
@Sourav: Add Facebook and it is :D – Piskvor left the building May 20 '11 at 16:51

score 1 · Answer 3 · answered May 20 '11 at 16:11

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You really should use RFC-822 compliant regexp instead - http://www.ex-parrot.com/~pdw/Mail-RFC822-Address.html

answered May 20 '11 at 16:11

Premature Optimization

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btw who coded that thing ? was it bill or mark or steve ? :O :0 – Sourav May 20 '11 at 16:14
1

@Sourav, according to the [credits](http://www.ex-parrot.com/~pdw/Mail-RFC822-Address/Mail-RFC822-Address.html#credits) name is Abigail – Premature Optimization May 20 '11 at 16:16
i was just joking :), but thats a realllllllllllllllly huge code ! – Sourav May 20 '11 at 16:18
@Sourav: None of those three are particularly great programmers, despite being successful businesmen, should you mean Gates, Zuckerberg and Jobs. – Piskvor left the building May 20 '11 at 16:18
@Piskvor Yup, but i think Bill is/was a good programmer :) – Sourav May 20 '11 at 16:19

How well does Stack Overflow's own e-mail validation regex work?

3 Answers3