What is the best regular expression for validating email addresses?

Question

Over the years I have slowly developed a regular expression that validates MOST email addresses correctly, assuming they don't use an IP address as the server part. Currently the expression is:

^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,4})$

I use this in several PHP programs, and it works most of the time. However, from time to time I get contacted by someone that is having trouble with a site that uses it, and I end up having to make some adjustment (most recently I realized that I wasn't allowing 4-character TLDs).

What's the best regular expression you have or have seen for validating emails?

I've seen several solutions that use functions that use several shorter expressions, but I'd rather have one long complex expression in a simple function instead of several short expression in a more complex function.

Answer 1

There's a good discussion here: http://www.regular-expressions.info/email.html

Answer 2

I use

\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*

Which is the one used in ASP.NET by the RegularExpressionValidator.

Answer 3

Don't know about best, but this one is at least correct, as long as the addresses have their comments stripped and replaced with whitespace.

Seriously. You should use an already written library for validating emails. The best way is probably to just send a verification e-mail to that address.

Answer 4

There are plenty examples of this out on the net (and I think even one that fully validates the RFC - but it's tens/hundreds of lines long if memory serves). People tend to get carried away validating this sort of thing. Why not just check it has an @ and at least one . and meets some simple minimum length. It's trivial to enter a fake email and still match any valid regex anyway. I would guess that false positives are better than false negatives.

Answer 5

I never bother creating with my own regular expression, because chances are that someone else has already come up with a better version. I always use regexlib to find one to my liking.

Answer 6

There is no good (and realistic, see Christian Vest Hansen's excellent reference) regular expression for this problem. The grammar (specified in RFC 5322) is too complicated for that. Use a real parser or, better, validate by trying (to send a message).

For PHP, there is Validate an E-Mail Address with PHP, the Right Way from which I quote "There is some danger that common usage and widespread sloppy coding will establish a de facto standard for e-mail addresses that is more restrictive than the recorded formal standard."

See also Validating Email Addresses, including the comments. Or Comparing E-mail Address Validating Regular Expressions.

Answer 7

For the love of SMTP, please remember that email address may contain a plus sign, which is typically used to add tags to an address. For example, [email protected], [email protected], and [email protected] all resolve to the same account. This allows recipients to sort their email based on the address it was sent to.

Your original regexp fails to allow the humble plus sign. For many of us, that means that we wouldn't register with your service - and probably won't stop to tell you why.

Answer 8

It all depends on how accurate you want to be. For my purposes, where I'm just trying to keep out things like "bob @ aol.com" or "steve" or "mary@aolcom", I use

/^\S+@\S+\.\S+$/

Sure, it will match things that aren't valid email addresses, but it's a matter of playing the 90/10 rule.

Answer 9

There is not one which is really usable.
I discuss some issues in my answer to Is there a php library for email address validation?, it is discussed also in Regexp recognition of email address hard?

In short, don't expect a single, usable regex to do a proper job. And the best regex will validate the syntax, not the validity of an e-mail ([email protected] is correct but it will probably bounce...).

Answer 10

While deciding which characters are allowed, please remember your apostrophed and hyphenated friends. I have no control over the fact that my company generates my email address using my name from the HR system. That includes the apostrophe in my last name. I can't tell you how many times I have been blocked from interacting with a website by the fact that my email address is "invalid".

Answer 11

Cal Henderson (Flickr) wrote an article called Parsing Email Adresses in PHP and shows how to do proper RFC (2)822-compliant Email Address parsing. You can also get the source code in php, python and ruby which is cc licensed.

Answer 12

I find the standard email validation from Visual Studio works fine for validating the user input, just helps cut down on use typos, but invalid email can stil be entered.

\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*

But i would always recomend performing a double optin for registration forms, so send the use an email and get them to click on link to active.

Answer 13

Don't.

You are guaranteed to get this wrong. Your users will be sad. You'll be sad.

Answer 14

Seems like this question gets asked a lot. I've worked at 4 different companies where someone at the help desk got yelled at by someone named O'Malley or O'Brien or some other e-mail address with an apostrophe. I'm not sure what the "best" solution is, but save yourself some hassle and accept an apostrophe.

--
bmb

Answer 15

This question is asked a lot, but I think you should step back and ask yourself why you want to validate email adresses syntactically? What is the benefit really?

• It will not catch common typos.
• It does not prevent people from entering invalid or made-up emails addresses, or entering someone elses address.

If you want to validate that an email is correct, you have no choice than to send an confirmation email and have the user reply to that. In many cases you will have to send a confirmation mail anyway for security reasons or for ethical reasons (so you cannot e.g sign someone up to a service against their will).

Answer 16

Strange that you "cannot" allow 4 characters TLDs. You are banning people from .info and .name, and the length limitation stop .travel and .museum, but yes, they are less common than 2 characters TLDs and 3 characters TLDs.

You should allow uppercase alphabets too. Email systems will normalize the local part and domain part.

For your regex of domain part, domain name cannot starts with '-' and cannot ends with '-'. Dash can only stays in between.

If you used the PEAR library, check out their mail function (forgot the exact name/library). You can validate email address by calling one function, and it validates the email address according to definition in RFC822.

Answer 17

We have used http://www.aspnetmx.com/ with a degree of success for a few years now. You can choose the level you want to validate at (e.g. syntax check, check for the domain, mx records or the actual email).

For front-end forms we generally verify that the domain exists and the syntax is correct, then we do stricter verification to clean out our database before doing bulk mail-outs.

Answer 18

The email addresses I want to validate are going to be used by an ASP.NET web application using the System.Net.Mail namespace to send emails to a list of people. So, rather than using some very complex regular expression, I just try to create a MailAddress instance from the address. The MailAddress construtor will throw an exception if the address is not formed properly. This way, I know I can at least get the email out of the door. Of course this is server-side validation but at a minimum you need that anyway.

protected void emailValidator_ServerValidate(object source, ServerValidateEventArgs args)
{
    try
    {
        var a = new MailAddress(txtEmail.Text);
    }
    catch (Exception ex)
    {
        args.IsValid = false;
        emailValidator.ErrorMessage = "email: " + ex.Message;
    }
}

Answer 19

is_email() remains, as far as I know, the only validator that will tell you definitively whether a given string is a valid email address or not. I've upload a new version at http://j.mp/isemail

I collated test cases from Cal Henderson, Dave Child, Phil Haack, Doug Lovell, RFC5322 and RFC 3696. 275 test addresses in all. I ran all these tests against all the free validators I could find.

I'll try to keep this page up-to-date as people enhance their validators. Thanks to Cal, Michael, Dave, Paul and Phil for their help and co-operation in compiling these tests and constructive criticism of my own validator.

People should be aware of the errata against RFC 3696 in particular. Three of the canonical examples are in fact invalid addresses. And the maximum length of an address is 254 or 256 characters, not 320.

Answer 20

It depends on what you mean by best: If you're talking about catching every valid email address use the following:

(?:(?:\r\n)?[ \t])*(?:(?:(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t]
)+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:
\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(
?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ 
\t]))*"(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\0
31]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\
](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+
(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:
(?:\r\n)?[ \t])*))*|(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z
|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)
?[ \t])*)*\<(?:(?:\r\n)?[ \t])*(?:@(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\
r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[
 \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)
?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t]
)*))*(?:,@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[
 \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*
)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t]
)+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*)
*:(?:(?:\r\n)?[ \t])*)?(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+
|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r
\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:
\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t
]))*"(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031
]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](
?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?
:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?
:\r\n)?[ \t])*))*\>(?:(?:\r\n)?[ \t])*)|(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?
:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?
[ \t]))*"(?:(?:\r\n)?[ \t])*)*:(?:(?:\r\n)?[ \t])*(?:(?:(?:[^()<>@,;:\\".\[\] 
\000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|
\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>
@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"
(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t]
)*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\
".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?
:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[
\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*|(?:[^()<>@,;:\\".\[\] \000-
\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(
?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)*\<(?:(?:\r\n)?[ \t])*(?:@(?:[^()<>@,;
:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([
^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\"
.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\
]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*(?:,@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\
[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\
r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] 
\000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]
|\\.)*\](?:(?:\r\n)?[ \t])*))*)*:(?:(?:\r\n)?[ \t])*)?(?:[^()<>@,;:\\".\[\] \0
00-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\
.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,
;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?
:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t])*
(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".
\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[
^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]
]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*\>(?:(?:\r\n)?[ \t])*)(?:,\s*(
?:(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\
".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)(?:\.(?:(
?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[
\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t
])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t
])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?
:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|
\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*|(?:
[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\
]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)*\<(?:(?:\r\n)
?[ \t])*(?:@(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["
()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)
?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>
@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*(?:,@(?:(?:\r\n)?[
 \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,
;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t]
)*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\
".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*)*:(?:(?:\r\n)?[ \t])*)?
(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".
\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)(?:\.(?:(?:
\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[
"()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])
*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])
+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\
.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z
|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*\>(?:(
?:\r\n)?[ \t])*))*)?;\s*)

(http://www.ex-parrot.com/~pdw/Mail-RFC822-Address.html) If you're looking for something simpler but that will catch most valid email addresses try something like:

"^[a-zA-Z0-9_.-]+@[a-zA-Z0-9-]+.[a-zA-Z0-9-.]+$"

EDIT: From the link: "This regular expression will only validate addresses that have had any comments stripped and replaced with whitespace (this is done by the module)." - Chas. Owens

Answer 21

There is a great little site that has various regular expressions and a testing environment, regexlib.com .

Answer 22

You could use the one employed by the jQuery Validation plugin:

/^((([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

Answer 23

For a vivid demonstration, the following monster is pretty good but still does not correctly recognize all syntactically valid email addresses: it recognizes nested comments up to four levels deep.

This is a job for a parser, but even if an address is syntactically valid, it still may not be deliverable. Sometimes you have to resort to the hillbilly method of "Hey, y'all, watch ee-us!"

// derivative of work with the following copyright and license:
// Copyright (c) 2004 Casey West.  All rights reserved.
// This module is free software; you can redistribute it and/or
// modify it under the same terms as Perl itself.

// see http://search.cpan.org/~cwest/Email-Address-1.80/

private static string gibberish = @"
(?-xism:(?:(?-xism:(?-xism:(?-xism:(?-xism:(?-xism:(?-xism:\
s*\((?:\s*(?-xism:(?-xism:(?>[^()\\]+))|(?-xism:\\(?-xism:[^
\x0A\x0D]))|(?-xism:\s*\((?:\s*(?-xism:(?-xism:(?>[^()\\]+))
|(?-xism:\\(?-xism:[^\x0A\x0D]))|)+)*\s*\)\s*))+)*\s*\)\s*)+
|\s+)*[^\x00-\x1F\x7F()<>\[\]:;@\,.<DQ>\s]+(?-xism:(?-xism:\
s*\((?:\s*(?-xism:(?-xism:(?>[^()\\]+))|(?-xism:\\(?-xism:[^
\x0A\x0D]))|(?-xism:\s*\((?:\s*(?-xism:(?-xism:(?>[^()\\]+))
|(?-xism:\\(?-xism:[^\x0A\x0D]))|)+)*\s*\)\s*))+)*\s*\)\s*)+
|\s+)*)|(?-xism:(?-xism:(?-xism:\s*\((?:\s*(?-xism:(?-xism:(
?>[^()\\]+))|(?-xism:\\(?-xism:[^\x0A\x0D]))|(?-xism:\s*\((?
:\s*(?-xism:(?-xism:(?>[^()\\]+))|(?-xism:\\(?-xism:[^\x0A\x
0D]))|)+)*\s*\)\s*))+)*\s*\)\s*)+|\s+)*<DQ>(?-xism:(?-xism:[
^\\<DQ>])|(?-xism:\\(?-xism:[^\x0A\x0D])))+<DQ>(?-xism:(?-xi
sm:\s*\((?:\s*(?-xism:(?-xism:(?>[^()\\]+))|(?-xism:\\(?-xis
m:[^\x0A\x0D]))|(?-xism:\s*\((?:\s*(?-xism:(?-xism:(?>[^()\\
]+))|(?-xism:\\(?-xism:[^\x0A\x0D]))|)+)*\s*\)\s*))+)*\s*\)\
s*)+|\s+)*))+)?(?-xism:(?-xism:(?-xism:\s*\((?:\s*(?-xism:(?
-xism:(?>[^()\\]+))|(?-xism:\\(?-xism:[^\x0A\x0D]))|(?-xism:
\s*\((?:\s*(?-xism:(?-xism:(?>[^()\\]+))|(?-xism:\\(?-xism:[
^\x0A\x0D]))|)+)*\s*\)\s*))+)*\s*\)\s*)+|\s+)*<(?-xism:(?-xi
sm:(?-xism:(?-xism:(?-xism:\s*\((?:\s*(?-xism:(?-xism:(?>[^(
)\\]+))|(?-xism:\\(?-xism:[^\x0A\x0D]))|(?-xism:\s*\((?:\s*(
?-xism:(?-xism:(?>[^()\\]+))|(?-xism:\\(?-xism:[^\x0A\x0D]))
|)+)*\s*\)\s*))+)*\s*\)\s*)+|\s+)*(?-xism:[^\x00-\x1F\x7F()<
>\[\]:;@\,.<DQ>\s]+(?:\.[^\x00-\x1F\x7F()<>\[\]:;@\,.<DQ>\s]
+)*)(?-xism:(?-xism:\s*\((?:\s*(?-xism:(?-xism:(?>[^()\\]+))
|(?-xism:\\(?-xism:[^\x0A\x0D]))|(?-xism:\s*\((?:\s*(?-xism:
(?-xism:(?>[^()\\]+))|(?-xism:\\(?-xism:[^\x0A\x0D]))|)+)*\s
*\)\s*))+)*\s*\)\s*)+|\s+)*)|(?-xism:(?-xism:(?-xism:\s*\((?
:\s*(?-xism:(?-xism:(?>[^()\\]+))|(?-xism:\\(?-xism:[^\x0A\x
0D]))|(?-xism:\s*\((?:\s*(?-xism:(?-xism:(?>[^()\\]+))|(?-xi
sm:\\(?-xism:[^\x0A\x0D]))|)+)*\s*\)\s*))+)*\s*\)\s*)+|\s+)*
<DQ>(?-xism:(?-xism:[^\\<DQ>])|(?-xism:\\(?-xism:[^\x0A\x0D]
)))+<DQ>(?-xism:(?-xism:\s*\((?:\s*(?-xism:(?-xism:(?>[^()\\
]+))|(?-xism:\\(?-xism:[^\x0A\x0D]))|(?-xism:\s*\((?:\s*(?-x
ism:(?-xism:(?>[^()\\]+))|(?-xism:\\(?-xism:[^\x0A\x0D]))|)+
)*\s*\)\s*))+)*\s*\)\s*)+|\s+)*))\@(?-xism:(?-xism:(?-xism:(
?-xism:\s*\((?:\s*(?-xism:(?-xism:(?>[^()\\]+))|(?-xism:\\(?
-xism:[^\x0A\x0D]))|(?-xism:\s*\((?:\s*(?-xism:(?-xism:(?>[^
()\\]+))|(?-xism:\\(?-xism:[^\x0A\x0D]))|)+)*\s*\)\s*))+)*\s
*\)\s*)+|\s+)*(?-xism:[^\x00-\x1F\x7F()<>\[\]:;@\,.<DQ>\s]+(
?:\.[^\x00-\x1F\x7F()<>\[\]:;@\,.<DQ>\s]+)*)(?-xism:(?-xism:
\s*\((?:\s*(?-xism:(?-xism:(?>[^()\\]+))|(?-xism:\\(?-xism:[
^\x0A\x0D]))|(?-xism:\s*\((?:\s*(?-xism:(?-xism:(?>[^()\\]+)
)|(?-xism:\\(?-xism:[^\x0A\x0D]))|)+)*\s*\)\s*))+)*\s*\)\s*)
+|\s+)*)|(?-xism:(?-xism:(?-xism:\s*\((?:\s*(?-xism:(?-xism:
(?>[^()\\]+))|(?-xism:\\(?-xism:[^\x0A\x0D]))|(?-xism:\s*\((
?:\s*(?-xism:(?-xism:(?>[^()\\]+))|(?-xism:\\(?-xism:[^\x0A\
x0D]))|)+)*\s*\)\s*))+)*\s*\)\s*)+|\s+)*\[(?:\s*(?-xism:(?-x
ism:[^\[\]\\])|(?-xism:\\(?-xism:[^\x0A\x0D])))+)*\s*\](?-xi
sm:(?-xism:\s*\((?:\s*(?-xism:(?-xism:(?>[^()\\]+))|(?-xism:
\\(?-xism:[^\x0A\x0D]))|(?-xism:\s*\((?:\s*(?-xism:(?-xism:(
?>[^()\\]+))|(?-xism:\\(?-xism:[^\x0A\x0D]))|)+)*\s*\)\s*))+
)*\s*\)\s*)+|\s+)*)))>(?-xism:(?-xism:\s*\((?:\s*(?-xism:(?-
xism:(?>[^()\\]+))|(?-xism:\\(?-xism:[^\x0A\x0D]))|(?-xism:\
s*\((?:\s*(?-xism:(?-xism:(?>[^()\\]+))|(?-xism:\\(?-xism:[^
\x0A\x0D]))|)+)*\s*\)\s*))+)*\s*\)\s*)+|\s+)*))|(?-xism:(?-x
ism:(?-xism:(?-xism:(?-xism:\s*\((?:\s*(?-xism:(?-xism:(?>[^
()\\]+))|(?-xism:\\(?-xism:[^\x0A\x0D]))|(?-xism:\s*\((?:\s*
(?-xism:(?-xism:(?>[^()\\]+))|(?-xism:\\(?-xism:[^\x0A\x0D])
)|)+)*\s*\)\s*))+)*\s*\)\s*)+|\s+)*(?-xism:[^\x00-\x1F\x7F()
<>\[\]:;@\,.<DQ>\s]+(?:\.[^\x00-\x1F\x7F()<>\[\]:;@\,.<DQ>\s
]+)*)(?-xism:(?-xism:\s*\((?:\s*(?-xism:(?-xism:(?>[^()\\]+)
)|(?-xism:\\(?-xism:[^\x0A\x0D]))|(?-xism:\s*\((?:\s*(?-xism
:(?-xism:(?>[^()\\]+))|(?-xism:\\(?-xism:[^\x0A\x0D]))|)+)*\
s*\)\s*))+)*\s*\)\s*)+|\s+)*)|(?-xism:(?-xism:(?-xism:\s*\((
?:\s*(?-xism:(?-xism:(?>[^()\\]+))|(?-xism:\\(?-xism:[^\x0A\
x0D]))|(?-xism:\s*\((?:\s*(?-xism:(?-xism:(?>[^()\\]+))|(?-x
ism:\\(?-xism:[^\x0A\x0D]))|)+)*\s*\)\s*))+)*\s*\)\s*)+|\s+)
*<DQ>(?-xism:(?-xism:[^\\<DQ>])|(?-xism:\\(?-xism:[^\x0A\x0D
])))+<DQ>(?-xism:(?-xism:\s*\((?:\s*(?-xism:(?-xism:(?>[^()\
\]+))|(?-xism:\\(?-xism:[^\x0A\x0D]))|(?-xism:\s*\((?:\s*(?-
xism:(?-xism:(?>[^()\\]+))|(?-xism:\\(?-xism:[^\x0A\x0D]))|)
+)*\s*\)\s*))+)*\s*\)\s*)+|\s+)*))\@(?-xism:(?-xism:(?-xism:
(?-xism:\s*\((?:\s*(?-xism:(?-xism:(?>[^()\\]+))|(?-xism:\\(
?-xism:[^\x0A\x0D]))|(?-xism:\s*\((?:\s*(?-xism:(?-xism:(?>[
^()\\]+))|(?-xism:\\(?-xism:[^\x0A\x0D]))|)+)*\s*\)\s*))+)*\
s*\)\s*)+|\s+)*(?-xism:[^\x00-\x1F\x7F()<>\[\]:;@\,.<DQ>\s]+
(?:\.[^\x00-\x1F\x7F()<>\[\]:;@\,.<DQ>\s]+)*)(?-xism:(?-xism
:\s*\((?:\s*(?-xism:(?-xism:(?>[^()\\]+))|(?-xism:\\(?-xism:
[^\x0A\x0D]))|(?-xism:\s*\((?:\s*(?-xism:(?-xism:(?>[^()\\]+
))|(?-xism:\\(?-xism:[^\x0A\x0D]))|)+)*\s*\)\s*))+)*\s*\)\s*
)+|\s+)*)|(?-xism:(?-xism:(?-xism:\s*\((?:\s*(?-xism:(?-xism
:(?>[^()\\]+))|(?-xism:\\(?-xism:[^\x0A\x0D]))|(?-xism:\s*\(
(?:\s*(?-xism:(?-xism:(?>[^()\\]+))|(?-xism:\\(?-xism:[^\x0A
\x0D]))|)+)*\s*\)\s*))+)*\s*\)\s*)+|\s+)*\[(?:\s*(?-xism:(?-
xism:[^\[\]\\])|(?-xism:\\(?-xism:[^\x0A\x0D])))+)*\s*\](?-x
ism:(?-xism:\s*\((?:\s*(?-xism:(?-xism:(?>[^()\\]+))|(?-xism
:\\(?-xism:[^\x0A\x0D]))|(?-xism:\s*\((?:\s*(?-xism:(?-xism:
(?>[^()\\]+))|(?-xism:\\(?-xism:[^\x0A\x0D]))|)+)*\s*\)\s*))
+)*\s*\)\s*)+|\s+)*))))(?-xism:\s*\((?:\s*(?-xism:(?-xism:(?
>[^()\\]+))|(?-xism:\\(?-xism:[^\x0A\x0D]))|(?-xism:\s*\((?:
\s*(?-xism:(?-xism:(?>[^()\\]+))|(?-xism:\\(?-xism:[^\x0A\x0
D]))|)+)*\s*\)\s*))+)*\s*\)\s*)*)"
  .Replace("<DQ>", "\"")
  .Replace("\t", "")
  .Replace(" ", "")
  .Replace("\r", "")
  .Replace("\n", "");

private static Regex mailbox =
  new Regex(gibberish, RegexOptions.ExplicitCapture);

Answer 24

this is one of the regex for email

^((([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])))\.?$

Answer 25

I am using this regex in .NET to validate email address.

^([A-Za-z0-9]|\{\}~]+)*)[\w,=!\-#|\$%\^&\*\+/\?{}~%5D">A-Za-z0-9@(?:[A-Za-z0-9-]+.)+[a-zA-Z]{2,9}$

One issue with it though..In the local name before the @ symbol, it accepts multiple periods in sequence.For example, [email protected].

Does anyone know how I can fix that and yet keep the rest of the logic intact?

Thanks

Answer 26

I don't believe the claim made by bortzmeyer, above, that "The grammar (specified in RFC 5322) is too complicated for that" (to be handled by a regular expression).

Here is the grammar: (http://tools.ietf.org/html/rfc5322#section-3.4.1)

addr-spec = local-part "@" domain local-part = dot-atom / quoted-string / obs-local-part domain = dot-atom / domain-literal / obs-domain domain-literal = [CFWS] "[" *([FWS] dtext) [FWS] "]" [CFWS] dtext = %d33-90 / ; Printable US-ASCII %d94-126 / ; characters not including obs-dtext ; "[", "]", or "\"

Assuming that dot-atom, quoted-string, obs-local-part, obs-domain are themselves regular languages, this is a very simple grammar. Just replace the local-part and domain in the addr-spec production with their respective productions, and you have a regular language, directly translatable to a regular expression.

Answer 27

One simple regular expression which would at least not reject any valid email address would be checking for something, followed by an @ sign and then something followed by a period and at least 2 somethings. It won't reject anything, but after reviewing the spec I can't find any email that would be valid and rejected.

email =~ /^[^@]+@[^@]+.[^@]{2}.*$/

This has the side effect of making sure that multiple @ symbols are not in the email as well.

Answer 28

RFC 5322 standard.

Note: Allows dot-atom local-part, quoted-string local-part, (internationalized) domain name domain, (IPv4, IPv6, and IPv4-mapped IPv6 address) domain literal domain, and (indefinitely/infinitely nested) CFWS.

Just 777 characters long.

'/^(?!(?>(?1)\x22?(?>\x22\x40|\x5C?[\x00-\x7F])\x22?){255,})(?!(?>(?1)\x22?\x5C?[\x00-\x7F]\x22?){65,}(?1)@)((?>(?>(?>((?>[\x09\x20]*\x0D\x0A)?[\x09\x20]+)?(\((?>(?2)?(?>(?>[\x21-\x27\x2A-\x5B\x5D-\x7E]|\x5C[\x20-\x7E]|(?3))))*(?2)?\)))+(?2)?)|(?2))?)([\x21\x23-\x27\x2A\x2B\x2D\x2F-\x39\x3D\x3F\x5E-\x7E]+|\x22(?>[\x01-\x08\x0B\x0C\x0E-\x21\x23-\x5B\x5D-\x7F]|\x5C[\x00-\x7F])*\x22)(?>(?1)\.(?1)(?4))*(?1)@(?1)(?>(?>\[(?:(?>IPv6:(?>(?>([a-f0-9]{1,4})(?>:(?5)){7})|(?>(?!(?:.*[a-f0-9][:\]]){8,})((?5)(?>:(?5)){0,6})?::(?6)?)))|(?>(?>IPv6:(?>(?>(?5)(?>:(?5)){5}:)|(?>(?!(?:.*[a-f0-9]:){6,})((?5)(?>:(?5)){0,4})?::(?>(?7):)?)))?(25[0-5]|2[0-4][0-9]|1[0-9]{2}|[1-9]?[0-9])(?>\.(?8)){3}))\])|(?>(?!.*(?1)[a-z0-9-]{64,})((?>xn--)?[a-z0-9]+(?>-[a-z0-9]+)*)(?>\.(?9)){0,126}))(?1)$/isD'

For a class which allows you to control which parts of the regex are used, check out Email Address Validation

Answer 29

No one mentioned the issue of localization (i18), what if you have clients coming from all over the world? You will need to then need to sub-categorize your regex per country/area, which I have seen developers ending up building a large dictionary/config. Detecting users' browser language setting may be a good starting point.

Answer 30

It's easy in perl 5.10 or newer:

/(?(DEFINE)
   (?<address>         (?&mailbox) | (?&group))
   (?<mailbox>         (?&name_addr) | (?&addr_spec))
   (?<name_addr>       (?&display_name)? (?&angle_addr))
   (?<angle_addr>      (?&CFWS)? < (?&addr_spec) > (?&CFWS)?)
   (?<group>           (?&display_name) : (?:(?&mailbox_list) | (?&CFWS))? ;
                                          (?&CFWS)?)
   (?<display_name>    (?&phrase))
   (?<mailbox_list>    (?&mailbox) (?: , (?&mailbox))*)

   (?<addr_spec>       (?&local_part) \@ (?&domain))
   (?<local_part>      (?&dot_atom) | (?&quoted_string))
   (?<domain>          (?&dot_atom) | (?&domain_literal))
   (?<domain_literal>  (?&CFWS)? \[ (?: (?&FWS)? (?&dcontent))* (?&FWS)?
                                 \] (?&CFWS)?)
   (?<dcontent>        (?&dtext) | (?&quoted_pair))
   (?<dtext>           (?&NO_WS_CTL) | [\x21-\x5a\x5e-\x7e])

   (?<atext>           (?&ALPHA) | (?&DIGIT) | [!#\$%&'*+-/=?^_`{|}~])
   (?<atom>            (?&CFWS)? (?&atext)+ (?&CFWS)?)
   (?<dot_atom>        (?&CFWS)? (?&dot_atom_text) (?&CFWS)?)
   (?<dot_atom_text>   (?&atext)+ (?: \. (?&atext)+)*)

   (?<text>            [\x01-\x09\x0b\x0c\x0e-\x7f])
   (?<quoted_pair>     \\ (?&text))

   (?<qtext>           (?&NO_WS_CTL) | [\x21\x23-\x5b\x5d-\x7e])
   (?<qcontent>        (?&qtext) | (?&quoted_pair))
   (?<quoted_string>   (?&CFWS)? (?&DQUOTE) (?:(?&FWS)? (?&qcontent))*
                        (?&FWS)? (?&DQUOTE) (?&CFWS)?)

   (?<word>            (?&atom) | (?&quoted_string))
   (?<phrase>          (?&word)+)

   # Folding white space
   (?<FWS>             (?: (?&WSP)* (?&CRLF))? (?&WSP)+)
   (?<ctext>           (?&NO_WS_CTL) | [\x21-\x27\x2a-\x5b\x5d-\x7e])
   (?<ccontent>        (?&ctext) | (?&quoted_pair) | (?&comment))
   (?<comment>         \( (?: (?&FWS)? (?&ccontent))* (?&FWS)? \) )
   (?<CFWS>            (?: (?&FWS)? (?&comment))*
                       (?: (?:(?&FWS)? (?&comment)) | (?&FWS)))

   # No whitespace control
   (?<NO_WS_CTL>       [\x01-\x08\x0b\x0c\x0e-\x1f\x7f])

   (?<ALPHA>           [A-Za-z])
   (?<DIGIT>           [0-9])
   (?<CRLF>            \x0d \x0a)
   (?<DQUOTE>          ")
   (?<WSP>             [\x20\x09])
 )

 (?&address)/x

Answer 31

Not to mention that non-Latin (Chinese, Arabic, Greek, Hebrew, Cyrillic and so on) domain names are to be allowed in the near future. Everyone has to change the email regex used, because those characters are surely not to be covered by [a-z]/i nor \w. They will all fail.

After all, the best way to validate the email address is still to actually send an email to the address in question to validate the address. If the email address is part of user authentication (register/login/etc), then you can perfectly combine it with the user activation system. I.e. send an email with a link with an unique activation key to the specified email address and only allow login when the user has activated the newly created account using the link in the email.

If the purpose of the regex is just to quickly inform the user in the UI that the specified email address doesn't look like in the right format, best is still to check if it matches basically the following regex:

^([^.@]+)(\.[^.@]+)*@([^.@]+\.)+([^.@]+)$

Simple as that. Why on earth would you care about the characters used in the name and domain? It's the client's responsibility to enter a valid email address, not the server's. Even when the client enters a syntactically valid email address like [email protected], this does not guarantee that it's a legit email address. No one regex can cover that.

Answer 32

This regex is from perl's Email::Valid I believe it to be the most accurate, it matches all 822. And, it is based on the regex in the O'Reilly book:

Regular expression built using Jeffrey Friedl's example in Mastering Regular Expressions (http://www.ora.com/catalog/regexp/).

$RFC822PAT = <<'EOF';
[\040\t]*(?:\([^\\\x80-\xff\n\015()]*(?:(?:\\[^\x80-\xff]|\([^\\\x80-\
xff\n\015()]*(?:\\[^\x80-\xff][^\\\x80-\xff\n\015()]*)*\))[^\\\x80-\xf
f\n\015()]*)*\)[\040\t]*)*(?:(?:[^(\040)<>@,;:".\\\[\]\000-\037\x80-\x
ff]+(?![^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff])|"[^\\\x80-\xff\n\015
"]*(?:\\[^\x80-\xff][^\\\x80-\xff\n\015"]*)*")[\040\t]*(?:\([^\\\x80-\
xff\n\015()]*(?:(?:\\[^\x80-\xff]|\([^\\\x80-\xff\n\015()]*(?:\\[^\x80
-\xff][^\\\x80-\xff\n\015()]*)*\))[^\\\x80-\xff\n\015()]*)*\)[\040\t]*
)*(?:\.[\040\t]*(?:\([^\\\x80-\xff\n\015()]*(?:(?:\\[^\x80-\xff]|\([^\
\\x80-\xff\n\015()]*(?:\\[^\x80-\xff][^\\\x80-\xff\n\015()]*)*\))[^\\\
x80-\xff\n\015()]*)*\)[\040\t]*)*(?:[^(\040)<>@,;:".\\\[\]\000-\037\x8
0-\xff]+(?![^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff])|"[^\\\x80-\xff\n
\015"]*(?:\\[^\x80-\xff][^\\\x80-\xff\n\015"]*)*")[\040\t]*(?:\([^\\\x
80-\xff\n\015()]*(?:(?:\\[^\x80-\xff]|\([^\\\x80-\xff\n\015()]*(?:\\[^
\x80-\xff][^\\\x80-\xff\n\015()]*)*\))[^\\\x80-\xff\n\015()]*)*\)[\040
\t]*)*)*@[\040\t]*(?:\([^\\\x80-\xff\n\015()]*(?:(?:\\[^\x80-\xff]|\([
^\\\x80-\xff\n\015()]*(?:\\[^\x80-\xff][^\\\x80-\xff\n\015()]*)*\))[^\
\\x80-\xff\n\015()]*)*\)[\040\t]*)*(?:[^(\040)<>@,;:".\\\[\]\000-\037\
x80-\xff]+(?![^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff])|\[(?:[^\\\x80-
\xff\n\015\[\]]|\\[^\x80-\xff])*\])[\040\t]*(?:\([^\\\x80-\xff\n\015()
]*(?:(?:\\[^\x80-\xff]|\([^\\\x80-\xff\n\015()]*(?:\\[^\x80-\xff][^\\\
x80-\xff\n\015()]*)*\))[^\\\x80-\xff\n\015()]*)*\)[\040\t]*)*(?:\.[\04
0\t]*(?:\([^\\\x80-\xff\n\015()]*(?:(?:\\[^\x80-\xff]|\([^\\\x80-\xff\
n\015()]*(?:\\[^\x80-\xff][^\\\x80-\xff\n\015()]*)*\))[^\\\x80-\xff\n\
015()]*)*\)[\040\t]*)*(?:[^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]+(?!
[^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff])|\[(?:[^\\\x80-\xff\n\015\[\
]]|\\[^\x80-\xff])*\])[\040\t]*(?:\([^\\\x80-\xff\n\015()]*(?:(?:\\[^\
x80-\xff]|\([^\\\x80-\xff\n\015()]*(?:\\[^\x80-\xff][^\\\x80-\xff\n\01
5()]*)*\))[^\\\x80-\xff\n\015()]*)*\)[\040\t]*)*)*|(?:[^(\040)<>@,;:".
\\\[\]\000-\037\x80-\xff]+(?![^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]
)|"[^\\\x80-\xff\n\015"]*(?:\\[^\x80-\xff][^\\\x80-\xff\n\015"]*)*")[^
()<>@,;:".\\\[\]\x80-\xff\000-\010\012-\037]*(?:(?:\([^\\\x80-\xff\n\0
15()]*(?:(?:\\[^\x80-\xff]|\([^\\\x80-\xff\n\015()]*(?:\\[^\x80-\xff][
^\\\x80-\xff\n\015()]*)*\))[^\\\x80-\xff\n\015()]*)*\)|"[^\\\x80-\xff\
n\015"]*(?:\\[^\x80-\xff][^\\\x80-\xff\n\015"]*)*")[^()<>@,;:".\\\[\]\
x80-\xff\000-\010\012-\037]*)*<[\040\t]*(?:\([^\\\x80-\xff\n\015()]*(?
:(?:\\[^\x80-\xff]|\([^\\\x80-\xff\n\015()]*(?:\\[^\x80-\xff][^\\\x80-
\xff\n\015()]*)*\))[^\\\x80-\xff\n\015()]*)*\)[\040\t]*)*(?:@[\040\t]*
(?:\([^\\\x80-\xff\n\015()]*(?:(?:\\[^\x80-\xff]|\([^\\\x80-\xff\n\015
()]*(?:\\[^\x80-\xff][^\\\x80-\xff\n\015()]*)*\))[^\\\x80-\xff\n\015()
]*)*\)[\040\t]*)*(?:[^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]+(?![^(\0
40)<>@,;:".\\\[\]\000-\037\x80-\xff])|\[(?:[^\\\x80-\xff\n\015\[\]]|\\
[^\x80-\xff])*\])[\040\t]*(?:\([^\\\x80-\xff\n\015()]*(?:(?:\\[^\x80-\
xff]|\([^\\\x80-\xff\n\015()]*(?:\\[^\x80-\xff][^\\\x80-\xff\n\015()]*
)*\))[^\\\x80-\xff\n\015()]*)*\)[\040\t]*)*(?:\.[\040\t]*(?:\([^\\\x80
-\xff\n\015()]*(?:(?:\\[^\x80-\xff]|\([^\\\x80-\xff\n\015()]*(?:\\[^\x
80-\xff][^\\\x80-\xff\n\015()]*)*\))[^\\\x80-\xff\n\015()]*)*\)[\040\t
]*)*(?:[^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]+(?![^(\040)<>@,;:".\\
\[\]\000-\037\x80-\xff])|\[(?:[^\\\x80-\xff\n\015\[\]]|\\[^\x80-\xff])
*\])[\040\t]*(?:\([^\\\x80-\xff\n\015()]*(?:(?:\\[^\x80-\xff]|\([^\\\x
80-\xff\n\015()]*(?:\\[^\x80-\xff][^\\\x80-\xff\n\015()]*)*\))[^\\\x80
-\xff\n\015()]*)*\)[\040\t]*)*)*(?:,[\040\t]*(?:\([^\\\x80-\xff\n\015(
)]*(?:(?:\\[^\x80-\xff]|\([^\\\x80-\xff\n\015()]*(?:\\[^\x80-\xff][^\\
\x80-\xff\n\015()]*)*\))[^\\\x80-\xff\n\015()]*)*\)[\040\t]*)*@[\040\t
]*(?:\([^\\\x80-\xff\n\015()]*(?:(?:\\[^\x80-\xff]|\([^\\\x80-\xff\n\0
15()]*(?:\\[^\x80-\xff][^\\\x80-\xff\n\015()]*)*\))[^\\\x80-\xff\n\015
()]*)*\)[\040\t]*)*(?:[^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]+(?![^(
\040)<>@,;:".\\\[\]\000-\037\x80-\xff])|\[(?:[^\\\x80-\xff\n\015\[\]]|
\\[^\x80-\xff])*\])[\040\t]*(?:\([^\\\x80-\xff\n\015()]*(?:(?:\\[^\x80
-\xff]|\([^\\\x80-\xff\n\015()]*(?:\\[^\x80-\xff][^\\\x80-\xff\n\015()
]*)*\))[^\\\x80-\xff\n\015()]*)*\)[\040\t]*)*(?:\.[\040\t]*(?:\([^\\\x
80-\xff\n\015()]*(?:(?:\\[^\x80-\xff]|\([^\\\x80-\xff\n\015()]*(?:\\[^
\x80-\xff][^\\\x80-\xff\n\015()]*)*\))[^\\\x80-\xff\n\015()]*)*\)[\040
\t]*)*(?:[^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]+(?![^(\040)<>@,;:".
\\\[\]\000-\037\x80-\xff])|\[(?:[^\\\x80-\xff\n\015\[\]]|\\[^\x80-\xff
])*\])[\040\t]*(?:\([^\\\x80-\xff\n\015()]*(?:(?:\\[^\x80-\xff]|\([^\\
\x80-\xff\n\015()]*(?:\\[^\x80-\xff][^\\\x80-\xff\n\015()]*)*\))[^\\\x
80-\xff\n\015()]*)*\)[\040\t]*)*)*)*:[\040\t]*(?:\([^\\\x80-\xff\n\015
()]*(?:(?:\\[^\x80-\xff]|\([^\\\x80-\xff\n\015()]*(?:\\[^\x80-\xff][^\
\\x80-\xff\n\015()]*)*\))[^\\\x80-\xff\n\015()]*)*\)[\040\t]*)*)?(?:[^
(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]+(?![^(\040)<>@,;:".\\\[\]\000-
\037\x80-\xff])|"[^\\\x80-\xff\n\015"]*(?:\\[^\x80-\xff][^\\\x80-\xff\
n\015"]*)*")[\040\t]*(?:\([^\\\x80-\xff\n\015()]*(?:(?:\\[^\x80-\xff]|
\([^\\\x80-\xff\n\015()]*(?:\\[^\x80-\xff][^\\\x80-\xff\n\015()]*)*\))
[^\\\x80-\xff\n\015()]*)*\)[\040\t]*)*(?:\.[\040\t]*(?:\([^\\\x80-\xff
\n\015()]*(?:(?:\\[^\x80-\xff]|\([^\\\x80-\xff\n\015()]*(?:\\[^\x80-\x
ff][^\\\x80-\xff\n\015()]*)*\))[^\\\x80-\xff\n\015()]*)*\)[\040\t]*)*(
?:[^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]+(?![^(\040)<>@,;:".\\\[\]\
000-\037\x80-\xff])|"[^\\\x80-\xff\n\015"]*(?:\\[^\x80-\xff][^\\\x80-\
xff\n\015"]*)*")[\040\t]*(?:\([^\\\x80-\xff\n\015()]*(?:(?:\\[^\x80-\x
ff]|\([^\\\x80-\xff\n\015()]*(?:\\[^\x80-\xff][^\\\x80-\xff\n\015()]*)
*\))[^\\\x80-\xff\n\015()]*)*\)[\040\t]*)*)*@[\040\t]*(?:\([^\\\x80-\x
ff\n\015()]*(?:(?:\\[^\x80-\xff]|\([^\\\x80-\xff\n\015()]*(?:\\[^\x80-
\xff][^\\\x80-\xff\n\015()]*)*\))[^\\\x80-\xff\n\015()]*)*\)[\040\t]*)
*(?:[^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]+(?![^(\040)<>@,;:".\\\[\
]\000-\037\x80-\xff])|\[(?:[^\\\x80-\xff\n\015\[\]]|\\[^\x80-\xff])*\]
)[\040\t]*(?:\([^\\\x80-\xff\n\015()]*(?:(?:\\[^\x80-\xff]|\([^\\\x80-
\xff\n\015()]*(?:\\[^\x80-\xff][^\\\x80-\xff\n\015()]*)*\))[^\\\x80-\x
ff\n\015()]*)*\)[\040\t]*)*(?:\.[\040\t]*(?:\([^\\\x80-\xff\n\015()]*(
?:(?:\\[^\x80-\xff]|\([^\\\x80-\xff\n\015()]*(?:\\[^\x80-\xff][^\\\x80
-\xff\n\015()]*)*\))[^\\\x80-\xff\n\015()]*)*\)[\040\t]*)*(?:[^(\040)<
>@,;:".\\\[\]\000-\037\x80-\xff]+(?![^(\040)<>@,;:".\\\[\]\000-\037\x8
0-\xff])|\[(?:[^\\\x80-\xff\n\015\[\]]|\\[^\x80-\xff])*\])[\040\t]*(?:
\([^\\\x80-\xff\n\015()]*(?:(?:\\[^\x80-\xff]|\([^\\\x80-\xff\n\015()]
*(?:\\[^\x80-\xff][^\\\x80-\xff\n\015()]*)*\))[^\\\x80-\xff\n\015()]*)
*\)[\040\t]*)*)*>)
EOF

Answer 33

For the most comprehensive evaluation of the best regular expression for validating an email address please see this link; "Comparing E-mail Address Validating Regular Expressions"

Here is the current top expression for reference purposes:

/^([\w\!\#$\%\&\'\*\+\-\/\=\?\^\`{\|\}\~]+\.)*[\w\!\#$\%\&\'\*\+\-\/\=\?\^\`{\|\}\~]+@((((([a-z0-9]{1}[a-z0-9\-]{0,62}[a-z0-9]{1})|[a-z])\.)+[a-z]{2,6})|(\d{1,3}\.){3}\d{1,3}(\:\d{1,5})?)$/i

Answer 34

<asp:TextBox ID="TextBox4" runat="server"></asp:TextBox>
        <asp:RegularExpressionValidator ID="RegularExpressionValidator1"  ControlToValidate="Textbox4" runat="server" 
        ErrorMessage="You must enter an email address" ValidationExpression="\w+([-+.]\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*"> </asp:RegularExpressionValidator>
        <asp:Button ID="Button3" runat="server" Text="CheckMail"/>

can you try this code....