diff --git a/EGroupwareMail.md b/EGroupwareMail.md
index 5fa123f..feef81e 100644
--- a/EGroupwareMail.md
+++ b/EGroupwareMail.md
@@ -54,6 +54,7 @@ password = your-secret-password
 ```
 services:
   mail:
+    hostname: <fully-qualified-hostname-as-used-in-certificate>
     volumes:
       # to use a recognized (not self-signed) certificate, add it here (certificate.pem is the certificate plus the chain!)
       # eg. to use the one created by LetsEncrypt's Certbot for the webserver use the following (replace your domain!)
@@ -61,6 +62,7 @@ services:
       - /etc/letsencrypt/live/egw.example.org/privkey.pem:/etc/dovecot/certificate.key
       - /etc/letsencrypt/live/egw.example.org/fullchain.pem:/etc/dovecot/certificate.pem
   smtp:
+    hostname: <fully-qualified-hostname-as-used-in-certificate>
     volumes:
       # to use a recognized (not self-signed) certificate, add it here (certificate.pem is the certificate plus the chain!)
       # eg. to use the one created by LetsEncrypt's Certbot for the webserver use the following (replace your domain!)