[Validator] added less-strict email host verification

New checkHost attribute in email constraint will
make the validator check for only one of MX, A or AAAA
DNS resource records to verify it as a valid
email address.

src/Symfony/Component/Validator/Constraints/Email.php

@@ -22,4 +22,5 @@ class Email extends Constraint
 {
     public $message = 'This value is not a valid email address';
     public $checkMX = false;
+    public $checkHost = false;
 }

src/Symfony/Component/Validator/Constraints/EmailValidator.php

@@ -51,9 +51,11 @@ class EmailValidator extends ConstraintValidator
                 $valid = false;
             }
 
-            // Check MX records
+            // Check for host DNS resource records
             if ($valid && $constraint->checkMX) {
                 $valid = $this->checkMX($host);
+            } else if ($valid && $constraint->checkHost) {
+                $valid = $this->checkHost($host);
             }
         }
 
@@ -69,7 +71,7 @@ class EmailValidator extends ConstraintValidator
     /**
      * Check DNS Records for MX type.
      *
-     * @param string $host Host name
+     * @param string $host Hostname
      *
      * @return Boolean
      */
@@ -77,4 +79,16 @@ class EmailValidator extends ConstraintValidator
     {
         return checkdnsrr($host, 'MX');
     }
+    
+    /**
+     * Check if one of MX, A or AAAA DNS RR exists.
+     *
+     * @param string $host Hostname
+     * 
+     * @return Boolean
+     */
+    private function checkHost($host)
+    {
+        return $this->checkMX($host) || (checkdnsrr($host, "A") || checkdnsrr($host, "AAAA"));
+    }
 }