diff --git a/README.md b/README.md
index 21ed5cae..bdbba2b8 100644
--- a/README.md
+++ b/README.md
@@ -111,7 +111,7 @@ terms), you do not want to do it several times.
 
 Possible SMTP options are the following:
 
- * **service** - a well known service identifier ("Gmail", "Hotmail" etc., see **Well known Services** for a list of supported services) to auto-configure host, port and secure connection settings
+ * **service** - an optional well known service identifier ("Gmail", "Hotmail" etc., see **Well known Services** for a list of supported services) to auto-configure host, port and secure connection settings
  * **host** - hostname of the SMTP server (defaults to "localhost", not needed with `service`)
  * **port** - port of the SMTP server (defaults to 25, not needed with `service`)
  * **secureConnection** - use SSL (default is `false`, not needed with `service`)