diff --git a/docs/content/faq.md b/docs/content/faq.md
index 09ef6c4c..dc8e1cad 100644
--- a/docs/content/faq.md
+++ b/docs/content/faq.md
@@ -257,6 +257,15 @@ Considering you want to delete all the e-mails received for `baduser@example.com
 baduser@example.com devnull
 ```
 
+!!! important
+    If you use a catch-all rule for the main/sub domain, you need another entry in `docker-data/dms/config/postfix-virtual.cf`:
+
+    ```cf
+    @mail.example.com hello@example.com
+    baduser@example.com devnull
+    devnull@mail.example.com devnull
+    ```
+
 ### How do I have more control about what SPAMASSASIN is filtering?
 
 By default, SPAM and INFECTED emails are put to a quarantine which is not very straight forward to access. Several config settings are affecting this behavior: