Minor changes, just coding style.

library/Respect/Validation/Exceptions/EmailException.php

@@ -10,7 +10,7 @@ class EmailException extends ValidationException
             self::STANDARD => '{{name}} must be valid email',
         ),
         self::MODE_NEGATIVE => array(
-            self::STANDARD => '{{name}} must not be email',
+            self::STANDARD => '{{name}} must not be an email',
         )
     );
 

library/Respect/Validation/Rules/Email.php

@@ -7,10 +7,7 @@ class Email extends AbstractRule
 
     public function validate($input)
     {
-       if (!is_string($input)) {
-           return false;
-       }
-
-        return (bool) filter_var($input, FILTER_VALIDATE_EMAIL);
+        return is_string($input) && filter_var($input, FILTER_VALIDATE_EMAIL);
     }
+
 }