我正在使用PHP 5.3.10版本。以下是代码：
<?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正确。
我认为只有一个字符的顶级域名是不正确的（根据这个列表：http://data.iana.org/TLD/tlds-alpha-by-domain.txt，我不知道有一个字符长度的顶级域名）。
那么，FILTER_VALIDATE_EMAIL过滤器是否正常工作？
FILTER_VALIDATE_EMAIL不支持PHP 5.2.14
验证电子邮件地址有点复杂。看一下这个列表：
有效的电子邮件地址
无效的电子邮件地址
Source http://en.wikipedia.org/wiki/Email_address
大多数所有的电子邮件验证实现都是“bug”，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：
Found on http://www.php.net/manual/en/filter.filters.validate.php
关于没有的“部分”地址。在域部分，源代码中的一条注释（在ext/filter/logical_filters.c中）证明了这种拒绝：
这里是Michael Rushton的类链接（链接已断，请参阅下面的源代码），它支持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; } }