Docs: Tips about server with multiple IP-addresses

docs/content/config/advanced/tips/server-multiple-ip-addresses.md

@@ -0,0 +1,43 @@
+---
+title: 'Advanced | Tips | Server with multiple IP-addresses'
+---
+
+## Server with multiple IP-addresses
+
+!!! warning "Only tested with docker configuration running with network-mode: host"
+
+    This configuration has only been tested with network: host where you have direct access to the host interfaces.
+
+If your host system is running multiple IPv4 and IPv6 IP-addresses, you probably have an interest to
+bind outgoing SMTP connections to specific IP-addresses to ensure MX records are aligned with
+PTR-records in DNS when sending emails to avoid getting blocked by SPF for example.
+
+We can use the tricks of [overriding defaults in postfix configuration](../override-defaults/postfix.md)
+by supplying a custom `docker-data/dms/config/postfix-master.cf` and `docker-data/dms/config/postfix-main.cf`.
+
+In `postfix-main.cf` you'll have to set the [smtp_bind_address](https://www.postfix.org/postconf.5.html#smtp_bind_address) and [smtp_bind_address6](https://www.postfix.org/postconf.5.html#smtp_bind_address6)
+to the respective IP-address on the server you want to use.
+
+!!! info "IP-addresses shown below are reserved documentation IP-addresses by IANA, [RFC-5737](https://datatracker.ietf.org/doc/rfc5737/) and [RFC-3849](https://datatracker.ietf.org/doc/html/rfc3849)."
+
+Example `postfix-main.cf`:
+
+```
+smtp_bind_address = 198.51.100.10
+smtp_bind_address6 = 2001:DB8::10
+```
+
+One problem with using `smtp_bind_address` is that the default configuration for `smtp-amavis` in
+DMS needs to be updated & explicit configured to connect via loopback (localhost) to avoid using
+the `smtp_bind_address` as source address when "forwarding" email for filtering via amavis.
+This seems to be a better configuration than adding your bind-addresses to `mynetworks` configuration in
+Postfix.
+
+Example `postfix-master.cf`:
+
+```
+smtp-amavis/unix/smtp_bind_address=127.0.0.1
+smtp-amavis/unix/smtp_bind_address6=::1
+```
+
+

docs/mkdocs.yml

@@ -153,6 +153,8 @@ nav:
         - 'IPv6': config/advanced/ipv6.md
         - 'Podman': config/advanced/podman.md
         - 'Dovecot Master Accounts': config/advanced/dovecot-master-accounts.md
+        - 'Tips':
+          - 'Server with multiple IP-addresses and docker configuration using network: host': config/advanced/tips/server-multiple-ip-addresses.md
   - 'Examples':
     - 'Tutorials':
       - 'Basic Installation': examples/tutorials/basic-installation.md