我使用的是 PHP 5.3.10。这是代码:

<?php
$email = "test@example.c";
if (filter_var($email, FILTER_VALIDATE_EMAIL))
        echo "Email: ".$email." correct";
else
        echo "email not correct";
?>

它返回:"Email: test@example.c correct.

我认为只有一个字符的顶级域是不正确的(根据此列表，我不知道一个字符长度的 TLD:http://data.iana.org/TLD/tlds-alpha-by-domain.txt).

那么，FILTER_VALIDATE_EMAIL 过滤器是否正常工作？

最佳答案

验证电子邮件地址有点复杂。 看看这个列表:

有效的电子邮件地址

1. niceandsimple@example.com
2. very.common@example.com
3. a.little.lengthy.but.fine@dept.example.com
4. disposable.style.email.with+symbol@example.com
5. 用户@[IPv6:2001:db8:1ff::a0b:dbd0]
6. “非常不寻常”@example.com
7. "very.unusual.@.unusual.com"@example.com
8. “非常.(),:;<>[]”.非常.”非常@\ "非常".unusual"@strange.example.com
9. postbox@com(顶级域是有效的主机名)
10. admin@mailserver1(没有顶级域名的本地域名)
11. !#$%&'*+-/=?^_`{}|~@example.org
12. "()<>[]:,;@\"!#$%&'*+-/=?^_`{}| ~.a"@example.org
13. ""@example.org(引号之间的空格)
14. üñîçøðé​​@example.com(本地部分为 Unicode 字符)

无效的电子邮件地址

1. Abc.example.com(@ 字符必须分隔本地和域 部分)
2. A@b@c@example.com(引号外只允许有一个@)
3. a"b(c)d,e:f;gi[j\k]l@example.com(没有特殊字符 在这个本地部分允许外引号)
4. just"not"right@example.com(引用的字符串必须用点分隔，或者 构成本地部分的唯一元素)
5. this is"not\allowed@example.com(空格、引号和反斜杠可能 仅存在于带引号的字符串中并以反斜杠开头)
6. this\still"not\allowed@example.com(即使转义(前面是 反斜杠)、空格、引号和反斜杠仍然必须 包含在引号中)

来源http://en.wikipedia.org/wiki/Email_address

几乎所有的电子邮件验证实现都存在“窃听”，但 php 实现可以很好地使用，因为它接受所有常见的电子邮件地址

更新:

发现于 http://www.php.net/manual/en/filter.filters.validate.php

关于没有 .在域部分，源代码中的注释(在 ext/filter/logical_filters.c 中)因此证明了这种拒绝:

 * The regex below is based on a regex by Michael Rushton.
 * However, it is not identical.  I changed it to only consider routeable
 * addresses as valid.  Michael's regex considers a@b a valid address
 * which conflicts with section 2.3.5 of RFC 5321 which states that:
 *
 *   Only resolvable, fully-qualified domain names (FQDNs) are permitted
 *   when domain names are used in SMTP.  In other words, names that can
 *   be resolved to MX RRs or address (i.e., A or AAAA) RRs (as discussed
 *   in Section 5) are permitted, as are CNAME RRs whose targets can be
 *   resolved, in turn, to MX or address RRs.  Local nicknames or
 *   unqualified names MUST NOT be used.

这里是 Michael Rushton 的类(class)链接(链接已损坏，请参阅下面的源代码) 同时支持 RFC 5321/5322

<?php
  /**
   * Squiloople Framework
   *
   * LICENSE: Feel free to use and redistribute this code.
   *
   * @author Michael Rushton <michael@squiloople.com>
   * @link http://squiloople.com/
   * @package Squiloople
   * @version 1.0
   * @copyright © 2012 Michael Rushton
   */
  /**
   * Email Address Validator
   *
   * Validate email addresses according to the relevant standards
   */
  final class EmailAddressValidator
  {
    // The RFC 5321 constant
    const RFC_5321 = 5321;
    // The RFC 5322 constant
    const RFC_5322 = 5322;
    /**
     * The email address
     *
     * @access private
     * @var string $_email_address
     */
    private $_email_address;
    /**
     * A quoted string local part is either allowed (true) or not (false)
     *
     * @access private
     * @var boolean $_quoted_string
     */
    private $_quoted_string = FALSE;
    /**
     * An obsolete local part is either allowed (true) or not (false)
     *
     * @access private
     * @var boolean $_obsolete
     */
    private $_obsolete = FALSE;
    /**
     * A basic domain name is either required (true) or not (false)
     *
     * @access private
     * @var boolean $_basic_domain_name
     */
    private $_basic_domain_name = TRUE;
    /**
     * A domain literal domain is either allowed (true) or not (false)
     *
     * @access private
     * @var boolean $_domain_literal
     */
    private $_domain_literal = FALSE;
   /**
     * Comments and folding white spaces are either allowed (true) or not (false)
     *
     * @access private
     * @var boolean $_cfws
     */
    private $_cfws = FALSE;
    /**
     * Set the email address and turn on the relevant standard if required
     *
     * @access public
     * @param string $email_address
     * @param null|integer $standard
     */
    public function __construct($email_address, $standard = NULL)
    {
      // Set the email address
      $this->_email_address = $email_address;
      // Set the relevant standard or throw an exception if an unknown is requested
      switch ($standard)
      {
        // Do nothing if no standard requested
        case NULL:
          break;
        // Otherwise if RFC 5321 requested
        case self::RFC_5321:
          $this->setStandard5321();
          break;
        // Otherwise if RFC 5322 requested
        case self::RFC_5322:
          $this->setStandard5322();
          break;
        // Otherwise throw an exception
        default:
          throw new Exception('Unknown RFC standard for email address validation.');
      }
    }
    /**
     * Call the constructor fluently
     *
     * @access public
     * @static
     * @param string $email_address
     * @param null|integer $standard
     * @return EmailAddressValidator
     */
    public static function setEmailAddress($email_address, $standard = NULL)
    {
      return new self($email_address, $standard);
    }
    /**
     * Validate the email address using a basic standard
     *
     * @access public
     * @return EmailAddressValidator
     */
    public function setStandardBasic()
    {
      // A quoted string local part is not allowed
      $this->_quoted_string = FALSE;
      // An obsolete local part is not allowed
      $this->_obsolete = FALSE;
      // A basic domain name is required
      $this->_basic_domain_name = TRUE;
      // A domain literal domain is not allowed
      $this->_domain_literal = FALSE;
      // Comments and folding white spaces are not allowed
      $this->_cfws = FALSE;
      // Return the EmailAddressValidator object
      return $this;
    }
    /**
     * Validate the email address using RFC 5321
     *
     * @access public
     * @return EmailAddressValidator
     */
    public function setStandard5321()
    {
      // A quoted string local part is allowed
      $this->_quoted_string = TRUE;
      // An obsolete local part is not allowed
      $this->_obsolete = FALSE;
      // Only a basic domain name is not required
      $this->_basic_domain_name = FALSE;
      // A domain literal domain is allowed
      $this->_domain_literal = TRUE;
      // Comments and folding white spaces are not allowed
      $this->_cfws = FALSE;
      // Return the EmailAddressValidator object
      return $this;
    }
    /**
     * Validate the email address using RFC 5322
     *
     * @access public
     * @return EmailAddressValidator
     */
    public function setStandard5322()
    {
      // A quoted string local part is disallowed
      $this->_quoted_string = FALSE;
      // An obsolete local part is allowed
      $this->_obsolete = TRUE;
      // Only a basic domain name is not required
      $this->_basic_domain_name = FALSE;
      // A domain literal domain is allowed
      $this->_domain_literal = TRUE;
      // Comments and folding white spaces are allowed
      $this->_cfws = TRUE;
      // Return the EmailAddressValidator object
      return $this;
    }
    /**
     * Either allow (true) or do not allow (false) a quoted string local part
     *
     * @access public
     * @param boolean $allow
     * @return EmailAddressValidator
     */
    public function setQuotedString($allow = TRUE)
    {
      // Either allow (true) or do not allow (false) a quoted string local part
      $this->_quoted_string = $allow;
      // Return the EmailAddressValidator object
      return $this;
    }
    /**
     * Either allow (true) or do not allow (false) an obsolete local part
     *
     * @access public
     * @param boolean $allow
     * @return EmailAddressValidator
     */
    public function setObsolete($allow = TRUE)
    {
      // Either allow (true) or do not allow (false) an obsolete local part
      $this->_obsolete = $allow;
      // Return the EmailAddressValidator object
      return $this;
    }
    /**
     * Either require (true) or do not require (false) a basic domain name
     *
     * @access public
     * @param boolean $allow
     * @return EmailAddressValidator
     */
    public function setBasicDomainName($allow = TRUE)
    {
      // Either require (true) or do not require (false) a basic domain name
      $this->_basic_domain_name = $allow;
      // Return the EmailAddressValidator object
      return $this;
    }
    /**
     * Either allow (true) or do not allow (false) a domain literal domain
     *
     * @access public
     * @param boolean $allow
     * @return EmailAddressValidator
     */
    public function setDomainLiteral($allow = TRUE)
    {
      // Either allow (true) or do not allow (false) a domain literal domain
      $this->_domain_literal = $allow;
      // Return the EmailAddressValidator object
      return $this;
    }
    /**
     * Either allow (true) or do not allow (false) comments and folding white spaces
     *
     * @access public
     * @param boolean $allow
     * @return EmailAddressValidator
     */
    public function setCFWS($allow = TRUE)
    {
      // Either allow (true) or do not allow (false) comments and folding white spaces
      $this->_cfws = $allow;
      // Return the EmailAddressValidator object
      return $this;
    }
    /**
     * Return the regular expression for a dot atom local part
     *
     * @access private
     * @return string
     */
    private function _getDotAtom()
    {
      return "([!#-'*+\/-9=?^-~-]+)(?>\.(?1))*";
    }
    /**
     * Return the regular expression for a quoted string local part
     *
     * @access private
     * @return string
     */
    private function _getQuotedString()
    {
      return '"(?>[ !#-\[\]-~]|\\\[ -~])*"';
    }
    /**
     * Return the regular expression for an obsolete local part
     *
     * @access private
     * @return string
     */
    private function _getObsolete()
    {
      return '([!#-\'*+\/-9=?^-~-]+|"(?>'
        . $this->_getFWS()
        . '(?>[\x01-\x08\x0B\x0C\x0E-!#-\[\]-\x7F]|\\\[\x00-\xFF]))*'
        . $this->_getFWS()
        . '")(?>'
        . $this->_getCFWS()
        . '\.'
        . $this->_getCFWS()
        . '(?1))*';
    }
    /**
     * Return the regular expression for a domain name domain
     *
     * @access private
     * @return string
     */
    private function _getDomainName()
    {
      // Return the basic domain name format if required
      if ($this->_basic_domain_name)
      {
        return '(?>' . $this->_getDomainNameLengthLimit()
          . '[a-z\d](?>[a-z\d-]*[a-z\d])?'
          . $this->_getCFWS()
          . '\.'
          . $this->_getCFWS()
          . '){1,126}[a-z]{2,6}';
      }
      // Otherwise return the full domain name format
      return $this->_getDomainNameLengthLimit()
        . '([a-z\d](?>[a-z\d-]*[a-z\d])?)(?>'
        . $this->_getCFWS()
        . '\.'
        . $this->_getDomainNameLengthLimit()
        . $this->_getCFWS()
        . '(?2)){0,126}';
    }
    /**
     * Return the regular expression for an IPv6 address
     *
     * @access private
     * @return string
     */
    private function _getIPv6()
    {
      return '([a-f\d]{1,4})(?>:(?3)){7}|(?!(?:.*[a-f\d][:\]]){8,})((?3)(?>:(?3)){0,6})?::(?4)?';
    }
    /**
     * Return the regular expression for an IPv4-mapped IPv6 address
     *
     * @access private
     * @return string
     */
    private function _getIPv4MappedIPv6()
    {
      return '(?3)(?>:(?3)){5}:|(?!(?:.*[a-f\d]:){6,})(?5)?::(?>((?3)(?>:(?3)){0,4}):)?';
    }
    /**
     * Return the regular expression for an IPv4 address
     *
     * @access private
     * @return string
     */
    private function _getIPv4()
    {
      return '(25[0-5]|2[0-4]\d|1\d{2}|[1-9]?\d)(?>\.(?6)){3}';
    }
    /**
     * Return the regular expression for a domain literal domain
     *
     * @access private
     * @return string
     */
    private function _getDomainLiteral()
    {
      return '\[(?:(?>IPv6:(?>'
        . $this->_getIPv6()
        . '))|(?>(?>IPv6:(?>'
        . $this->_getIPv4MappedIPv6()
        . '))?'
        . $this->_getIPv4()
        . '))\]';
    }
    /**
     * Return either the regular expression for folding white spaces or its backreference
     *
     * @access private
     * @param boolean $define
     * @return string
     */
    private function _getFWS($define = FALSE)
    {
      // Return the backreference if $define is set to FALSE otherwise return the regular expression
      if ($this->_cfws)
      {
        return !$define ? '(?P>fws)' : '(?<fws>(?>(?>(?>\x0D\x0A)?[\t ])+|(?>[\t ]*\x0D\x0A)?[\t ]+)?)';
      }
    }
    /**
     * Return the regular expression for comments
     *
     * @access private
     * @return string
     */
    private function _getComments()
    {
      return '(?<comment>\((?>'
        . $this->_getFWS()
        . '(?>[\x01-\x08\x0B\x0C\x0E-\'*-\[\]-\x7F]|\\\[\x00-\x7F]|(?P>comment)))*'
        . $this->_getFWS()
        . '\))';
    }
    /**
     * Return either the regular expression for comments and folding white spaces or its backreference
     *
     * @access private
     * @param boolean $define
     * @return string
     */
    private function _getCFWS($define = FALSE)
    {
      // Return the backreference if $define is set to FALSE
      if ($this->_cfws && !$define)
      {
        return '(?P>cfws)';
      }
      // Otherwise return the regular expression
      if ($this->_cfws)
      {
        return '(?<cfws>(?>(?>(?>'
          . $this->_getFWS(TRUE)
          . $this->_getComments()
          . ')+'
          . $this->_getFWS()
          . ')|'
          . $this->_getFWS()
          . ')?)';
      }
    }
    /**
     * Establish and return the valid format for the local part
     *
     * @access private
     * @return string
     */
    private function _getLocalPart()
    {
      // The local part may be obsolete if allowed
      if ($this->_obsolete)
      {
        return $this->_getObsolete();
      }
      // Otherwise the local part must be either a dot atom or a quoted string if the latter is allowed
      if ($this->_quoted_string)
      {
        return '(?>' . $this->_getDotAtom() . '|' . $this->_getQuotedString() . ')';
      }
      // Otherwise the local part must be a dot atom
      return $this->_getDotAtom();
    }
    /**
     * Establish and return the valid format for the domain
     *
     * @access private
     * @return string
     */
    private function _getDomain()
    {
      // The domain must be either a domain name or a domain literal if the latter is allowed
      if ($this->_domain_literal)
      {
        return '(?>' . $this->_getDomainName() . '|' . $this->_getDomainLiteral() . ')';
      }
      // Otherwise the domain must be a domain name
      return $this->_getDomainName();
    }
    /**
     * Return the email address length limit
     *
     * @access private
     * @return string
     */
    private function _getEmailAddressLengthLimit()
    {
      return '(?!(?>' . $this->_getCFWS() . '"?(?>\\\[ -~]|[^"])"?' . $this->_getCFWS() . '){255,})';
    }
    /**
     * Return the local part length limit
     *
     * @access private
     * @return string
     */
    private function _getLocalPartLengthLimit()
    {
      return '(?!(?>' . $this->_getCFWS() . '"?(?>\\\[ -~]|[^"])"?' . $this->_getCFWS() . '){65,}@)';
    }
    /**
     * Establish and return the domain name length limit
     *
     * @access private
     * @return string
     */
    private function _getDomainNameLengthLimit()
    {
      return '(?!' . $this->_getCFWS() . '[a-z\d-]{64,})';
    }
    /**
     * Check to see if the domain can be resolved to MX RRs
     *
     * @access private
     * @param array $domain
     * @return integer|boolean
     */
    private function _verifyDomain($domain)
    {
      // Return 0 if the domain cannot be resolved to MX RRs
      if (!checkdnsrr(end($domain), 'MX'))
      {
        return 0;
      }
      // Otherwise return true
      return TRUE;
    }
    /**
     * Perform the validation check on the email address's syntax and, if required, call _verifyDomain()
     *
     * @access public
     * @param boolean $verify
     * @return boolean|integer
     */
    public function isValid($verify = FALSE)
    {
      // Return false if the email address has an incorrect syntax
      if (!preg_match(
          '/^'
        . $this->_getEmailAddressLengthLimit()
        . $this->_getLocalPartLengthLimit()
        . $this->_getCFWS()
        . $this->_getLocalPart()
        . $this->_getCFWS()
        . '@'
        . $this->_getCFWS()
        . $this->_getDomain()
        . $this->_getCFWS(TRUE)
        . '$/isD'
        , $this->_email_address
      ))
      {
        return FALSE;
      }
      // Otherwise check to see if the domain can be resolved to MX RRs if required
      if ($verify)
      {
        return $this->_verifyDomain(explode('@', $this->_email_address));
      }
      // Otherwise return 1
      return 1;
    }
  }

关于PHP FILTER_VALIDATE_EMAIL 无法正常工作，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/19220158/