diff --git a/README.md b/README.md
index 0e7126b..bb63f32 100644
--- a/README.md
+++ b/README.md
@@ -2617,6 +2617,10 @@ the messages received by the SMTP server can be reproduced in JSON format.
When both the SMTP server and the HTTP server are enabled, the following
additional endpoints are made available on the HTTP server:
+#### /smtp/gui
+A very basic HTML/JavaScript GUI that displays and auto-refreshes the received
+messages is made available on the `/smtp/gui` endpoint.
+
#### /smtp
On the `/smtp` endpoint, an index of all received messages will be made
available as JSON in the following schema:
diff --git a/internal/smtp/gui.html b/internal/smtp/gui.html
new file mode 100644
index 0000000..8107a38
--- /dev/null
+++ b/internal/smtp/gui.html
@@ -0,0 +1,129 @@
+
+
+