Added FAQ about SMTP Banner

docs/faq.rst

@@ -253,7 +253,7 @@ correct syntax. The following file names will be taken as override configuration
 - `Nginx`_ - All ``*.conf`` files in the ``nginx`` sub-directory;
 - `Rspamd`_ - All files in the ``rspamd`` sub-directory.
 
-*Issue reference:* `206`_.
+*Issue reference:* `206`_, `1368`_.
 
 I want to integrate Nextcloud 15 (and newer) with Mailu
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@@ -353,6 +353,15 @@ down and up again. A container restart is not sufficient.
 
 *Issue reference:* `615`_.
 
+SMTP Banner from overrides/postfix.cf is ignored
+````````````````````````````````````````````````
+
+Any mail related connection is proxied by nginx. Therefore the SMTP Banner is also set by nginx. Overwriting in overrides/postfix.cf does not apply. If you want to change the hostname in the SMTP Banner greeting, you must change the first entry of HOSTNAMES in mailu.env.
+
+*Issue reference:* `1368`_.
+
+.. _`1368`: https://github.com/Mailu/Mailu/issues/1368
+
 403 - Access Denied Errors
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