diff --git a/src/svxlink/svxlink/contrib/TetraLogic/README.adoc b/src/svxlink/svxlink/contrib/TetraLogic/README.adoc
index 5c6a2b1b..f0c8a855 100644
--- a/src/svxlink/svxlink/contrib/TetraLogic/README.adoc
+++ b/src/svxlink/svxlink/contrib/TetraLogic/README.adoc
@@ -73,6 +73,9 @@ from svxlink.conf. This file is now located in /etc/svxlink/svxlink.d directory.
 Remove the [TetraLogic]-section from svxlink.conf but let the LOGICS- and LINKS
 definitions with "Tetra" untouched.
 
+To use the QOS (quality of service) funtionality the installation and configuration
+of ssmtp is needed.
+
 == Documentation ==
 - manpage svxlink.conf.5
 - German pdf is available here: https://github.com/dl1hrc/documentation