diff --git a/README.md b/README.md
index 732a7aa..7104171 100644
--- a/README.md
+++ b/README.md
@@ -8,7 +8,7 @@ Features
 
 * STARTTLS (using `crypto/tls`)
 * Authentication (PLAIN/LOGIN, only after STARTTLS)
-* XCLIENT (for running behind a proxy)
+* [XCLIENT](http://www.postfix.org/XCLIENT_README.html) and [PROXY protocol](https://www.haproxy.org/download/1.8/doc/proxy-protocol.txt) (for running behind a proxy)
 * Connection, HELO, sender and recipient checks for rejecting e-mails using callbacks
 * Configurable limits for: connection count, message size and recipient count
 * Hands incoming e-mail off to a configured callback function