Email regular expression

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What is the best regular expression for validating email addresses?

Duplicate: What is the best regular expression for validating email addresses?

I know this is a common question, but I still can't seem to find a great regular expression to use when validating email addresses.

I don't really have time to go read the spec and write my own. What have ya'll used before, and has it worked well? I don't really care about 100% matching the spec, but the closer the better.

There are plenty of questions about email regex. http://stackoverflow.com/questions/508108/regex-for-email-validation-closed — Macarse, Jun 15 '09 at 16:39

score 14 · Accepted Answer · edited Oct 07 '21 at 05:49

Here's a function that I use. It does a little more than just run the email address through a regex, but so far it is the most complete solution that I found:

function validEmail($email, $skipDNS = false)
{
   $isValid = true;
   $atIndex = strrpos($email, "@");
   if (is_bool($atIndex) && !$atIndex)
   {
      $isValid = false;
   }
   else
   {
      $domain = substr($email, $atIndex+1);
      $local = substr($email, 0, $atIndex);
      $localLen = strlen($local);
      $domainLen = strlen($domain);
      if ($localLen < 1 || $localLen > 64)
      {
         // local part length exceeded
         $isValid = false;
      }
      else if ($domainLen < 1 || $domainLen > 255)
      {
         // domain part length exceeded
         $isValid = false;
      }
      else if ($local[0] == '.' || $local[$localLen-1] == '.')
      {
         // local part starts or ends with '.'
         $isValid = false;
      }
      else if (preg_match('/\\.\\./', $local))
      {
         // local part has two consecutive dots
         $isValid = false;
      }
      else if (!preg_match('/^[A-Za-z0-9\\-\\.]+$/', $domain))
      {
         // character not valid in domain part
         $isValid = false;
      }
      else if (preg_match('/\\.\\./', $domain))
      {
         // domain part has two consecutive dots
         $isValid = false;
      }
      else if (!preg_match('/^(\\\\.|[A-Za-z0-9!#%&`_=\\/$\'*+?^{}|~.-])+$/', str_replace("\\\\","",$local)))
      {
         // character not valid in local part unless 
         // local part is quoted
         if (!preg_match('/^"(\\\\"|[^"])+"$/', str_replace("\\\\","",$local)))
         {
            $isValid = false;
         }
      }
      
      if(!$skipDNS)
      {
          if ($isValid && !(checkdnsrr($domain,"MX") || checkdnsrr($domain,"A")))
          {
             // domain not found in DNS
             $isValid = false;
          }
      }
   }
   return $isValid;
}

The function has an optional $skipDNS argument that can be set to TRUE if you don't want to validate the MX records for the hos. Otherwise the function will attempt to validate that the e-mail address provided actually maps to a real email server.

It's useful to note that most RegEx email validation techniques will validate most e-mail addresses but they will most likely allow some carefully crafted invalid addresses or worst.. fail on some more obscure, but valid e-mail addresses. For more information you may want to check out the Internet Message Formats RFC which describes the allowed format for e-mail addresses.

This is actually also somewhat vulnerable to REDOS. See a related exploit here: https://github.com/johnhenry/valid-email/issues/4 — James Davis, Feb 22 '18 at 03:05

score 13 · Answer 2 · edited Jun 15 '09 at 16:39

13

^([0-9a-zA-Z]([-\.\w]*[0-9a-zA-Z])*@([0-9a-zA-Z][-\w]*[0-9a-zA-Z]\.)+[a-zA-Z]{2,9})$

This is an awesome tool to help write and check expression, not sure if you have it but hopefully its helpful.

Expresso

edited Jun 15 '09 at 16:39

ysth

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answered Jun 15 '09 at 16:34

Gabe

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This regex is a sure-fire way to induce catastrophic backtracking, as evidenced by [this follow-up question](http://stackoverflow.com/q/13087755/20670). – Tim Pietzcker Oct 26 '12 at 13:34
2

Don't use this - see: http://stackoverflow.com/questions/13087755/can-anyone-tell-me-why-this-c-sharp-email-validation-regular-expression-regex – Jon Rea Oct 26 '12 at 13:40
`Awesome tool` doesn't warn about catastrophic backtracking. Not sure if RegexBuddy does, but it's my tool of choice. – Kevin Mark Nov 10 '13 at 08:11

Email regular expression

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