Use enable_ipv6 to fully disable iPv6

docs/firststeps-disable_ipv6.md

@@ -0,0 +1,22 @@
+This is **NOT** recommended!
+
+If IPv6 MUST be disabled to fit a network, open `docker-compose.yml`, search for `enable_ipv6`...
+
+
+```
+networks:
+  mailcow-network:
+    [...]
+    enable_ipv6: true
+    [...]
+```
+
+...change it to `enable_ipv6: false`.
+
+mailcow needs to be shutdown, the containers removed and the network recreated:
+
+```
+docker-compose down
+docker-compose up -d
+```
+

mkdocs.yml

@@ -29,6 +29,7 @@ pages:
   - 'Rspamd Web UI': 'firststeps-rspamd_ui.md'
   - 'Reverse Proxy': 'firststeps-rp.md'
   - 'SNAT': 'firststeps-snat.md'
+  - 'Disable IPv6': 'firststeps-disable_ipv6.md'
   - 'Setup a relayhost': 'firststeps-relayhost.md'
   - 'Logging': 'firststeps-logging.md'
   - 'Local MTA on Docker host': 'firststeps-local_mta.md'