Updated EmailField length to support long domains (#243)

mongoengine/fields.py

@@ -143,7 +143,7 @@ class EmailField(StringField):
     EMAIL_REGEX = re.compile(
         r"(^[-!#$%&'*+/=?^_`{}|~0-9A-Z]+(\.[-!#$%&'*+/=?^_`{}|~0-9A-Z]+)*"  # dot-atom
         r'|^"([\001-\010\013\014\016-\037!#-\[\]-\177]|\\[\001-011\013\014\016-\177])*"'  # quoted-string
-        r')@(?:[A-Z0-9](?:[A-Z0-9-]{0,61}[A-Z0-9])?\.)+[A-Z]{2,6}\.?$', re.IGNORECASE  # domain
+        r')@(?:[A-Z0-9](?:[A-Z0-9-]{0,253}[A-Z0-9])?\.)+[A-Z]{2,6}\.?$', re.IGNORECASE  # domain
     )
 
     def validate(self, value):