diff --git a/README.md b/README.md
index bc778ad..d3888fd 100644
--- a/README.md
+++ b/README.md
@@ -11,9 +11,14 @@ To use this library, add the following to your `Cargo.toml`:
 
 ```toml
 [dependencies]
-lettre = "0.4"
+lettre = "0.5"
 ```
 
+Testing
+-------
+
+The tests require a mail server listening locally on port 25.
+
 License
 -------