diff --git a/README.md b/README.md
index 21472bc..0f1ed01 100644
--- a/README.md
+++ b/README.md
@@ -11,3 +11,4 @@ Information about how to configure email servers, services, etc.
 - https://ssl-tools.net/
 - https://www.nospamproxy.de/wp-content/uploads/Praxisleitfaden-DKIM-SPF-DMARC-DANE-1.pdf
 - https://www.debouncer.com/reverse-dns-check
+- https://www.checktls.com/index.html