PHP: Email Validation (RFC 2822)

valid_email.php

/**
 * Verifies the syntax of the given e-mail address.
 *
 * See RFC 2822 for details.
 *
 * @param $mail
 *   A string containing an e-mail address.
 *
 * @return
 *   1 if the email address is valid, 0 if it is invalid or empty, and FALSE if
 *   there is an input error (such as passing in an array instead of a string).
 */
function valid_email_address($mail)
{
	$user   = '[a-zA-Z0-9_\-\.\+\^!#\$%&*+\/\=\?\`\|\{\}~\']+';
	$domain = '(?:(?:[a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]*[a-zA-Z0-9])\.?)+';
	$ipv4   = '[0-9]{1,3}(\.[0-9]{1,3}){3}';
	$ipv6   = '[0-9a-fA-F]{1,4}(\:[0-9a-fA-F]{1,4}){7}';

	return preg_match("/^$user@($domain|(\[($ipv4|$ipv6)\]))$/", $mail);
}

Very useful. Have you considered contributing to get PHP's filter_var to follow RFC 2822 and not RFC 822?

how to void dot in [email protected]?

Above function could not validate emails like John Smith [email protected] which is a standard format of RFC 2822
I have created a function which will validate both.

function validate_email($email) {
  $email_matches = array();

  $from_regex   = '[a-zA-Z0-9_,\s\-\.\+\^!#\$%&*+\/\=\?\`\|\{\}~\']+';
  $user_regex   = '[a-zA-Z0-9_\-\.\+\^!#\$%&*+\/\=\?\`\|\{\}~\']+';
  $domain_regex = '(?:(?:[a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]*[a-zA-Z0-9])\.?)+';
  $ipv4_regex   = '[0-9]{1,3}(\.[0-9]{1,3}){3}';
  $ipv6_regex   = '[0-9a-fA-F]{1,4}(\:[0-9a-fA-F]{1,4}){7}';

  preg_match("/^$from_regex\s\<(($user_regex)@($domain_regex|(\[($ipv4_regex|$ipv6_regex)\])))\>$/", $email, $matches_2822);
  preg_match("/^($user_regex)@($domain_regex|(\[($ipv4_regex|$ipv6_regex)\]))$/", $email, $matches_normal);

  // Check for valid email as per RFC 2822 spec.
  if (empty($matches_normal) && !empty($matches_2822) && !empty($matches_2822[3])) {
    $email_matches['from_name'] = $matches_2822[0];
    $email_matches['full_email'] = $matches_2822[1];
    $email_matches['email_name'] = $matches_2822[2];
    $email_matches['domain'] = $matches_2822[3];
  }

  // Check for valid email as per RFC 822 spec.
  if (empty($matches_2822) && !empty($matches_normal) && !empty($matches_normal[2])) {
    $email_matches['from_name'] = '';
    $email_matches['full_email'] = $matches_normal[0];
    $email_matches['email_name'] = $matches_normal[1];
    $email_matches['domain'] = $matches_normal[2];
  }

  return $email_matches;
}