Merge pull request #63 from shaneonabike/patch-1

Update pre-req documentation

docs/prerequesite-system.md

@@ -4,7 +4,8 @@ Before you run **mailcow: dockerized**, there are a few requirements that you sh
     When running mailcow: dockerized on a Debian 8 (Jessie) box, you should [switch to kernel 4.9 from Jessie backports](https://packages.debian.org/jessie-backports/linux-image-amd64) to avoid a bug when running Docker containers with *healthchecks*! For more details read: [github.com/docker/docker/issues/30402](https://github.com/docker/docker/issues/30402)
 
 !!! info
-    - mailcow: dockerized requires [some ports](#default-ports) to be open for incomming connections, so make sure that your firewall is not bloking these. Also make sure that no other application is interferring with mailcow's configuration.
+    - mailcow: dockerized requires [some ports](#default-ports) to be open for incoming connections, so make sure that your firewall is not blocking these.
+    - Make sure that no other application is interferring with mailcow's configuration, such as another mail service
     - A correct DNS setup is crucial to every good mailserver setup, so please make sure you got at least the [basics](prerequesite-dns/#the-minimal-dns-configuration) covered before you begin!
     - Make sure that your system has a correct date and [time setup](#date-and-time). This is crucial for stuff like two factor TOTP authentication.
 
@@ -51,6 +52,18 @@ To bind a service to an IP address, you can prepend the IP like this: `SMTP_PORT
 
 **Important**: You cannot use IP:PORT bindings in HTTP_PORT and HTTPS_PORT. Please use `HTTP_PORT=1234` and `HTTP_BIND=1.2.3.4` instead.
 
+To unblock firewalls using ufw you can use the following commands:
+```
+# ufw allow 25
+# ufw allow 80
+# ufw allow 110
+# ufw allow 143
+# ufw allow 443
+# ufw allow 465
+# ufw allow 587
+# ufw allow 993
+# ufw allow 995
+```
 
 ## Date and Time