diff --git a/docs/content/tutorials/installation-examples.md b/docs/content/tutorials/installation-examples.md
index a267a67d..b84447fa 100644
--- a/docs/content/tutorials/installation-examples.md
+++ b/docs/content/tutorials/installation-examples.md
@@ -1,5 +1,7 @@
 ## Building a simple mailserver
 
+**WARNING**: Adding the docker network's gateway to the list of trusted hosts, e.g. using the `network` or `connected-networks` option, can create an [**open relay**](https://en.wikipedia.org/wiki/Open_mail_relay), [for instance](https://github.com/tomav/docker-mailserver/issues/1405#issuecomment-590106498) if IPv6 is enabled on the host machine but not in Docker. ([#1405](https://github.com/tomav/docker-mailserver/issues/1405))
+
 We are going to use this docker based mailserver:
 
 - First create a directory for the mailserver and get the setup script: