Added a caution note about the checkMX option

javiereguiluz · javiereguiluz · commit 7910bf4b9d49 · 2018-10-05T15:37:28.000+02:00
diff --git a/reference/constraints/Email.rst b/reference/constraints/Email.rst
@@ -117,6 +117,11 @@ checkMX
 If true, then the :phpfunction:`checkdnsrr` PHP function will be used to
 check the validity of the MX record of the host of the given email.
 
+.. caution::
+
+    This option is not reliable because it depends on the network conditions
+    and some valid servers refuse to respond to those requests.
+
 checkHost
 ~~~~~~~~~
 
