docs(refactor): Restructure document hierarchy

Additionally rename `installation-examples.md` and split

docs/content/config/advanced/override-defaults/dovecot.md

@@ -0,0 +1,59 @@
+---
+title: 'Override the Default Configs | Dovecot'
+---
+
+## Add Configuration
+
+The Dovecot default configuration can easily be extended providing a `config/dovecot.cf` file.
+[Dovecot documentation](https://wiki.dovecot.org) remains the best place to find configuration options.
+
+Your `docker-mailserver` folder should look like this example:
+
+```txt
+├── config
+│   ├── dovecot.cf
+│   ├── postfix-accounts.cf
+│   └── postfix-virtual.cf
+├── docker-compose.yml
+└── README.md
+```
+
+One common option to change is the maximum number of connections per user:
+
+```cf
+mail_max_userip_connections = 100
+```
+
+Another important option is the `default_process_limit` (defaults to `100`). If high-security mode is enabled you'll need to make sure this count is higher than the maximum number of users that can be logged in simultaneously.
+
+This limit is quickly reached if users connect to the mail server with multiple end devices.
+
+## Override Configuration
+
+For major configuration changes it’s best to override the dovecot configuration files. For each configuration file you want to override, add a list entry under the `volumes` key.
+
+```yaml
+services:
+  mail:
+    volumes:
+      - maildata:/var/mail
+      - ./config/dovecot/10-master.conf:/etc/dovecot/conf.d/10-master.conf
+```
+
+## Debugging
+
+To debug your dovecot configuration you can use:
+
+- This command: `./setup.sh debug login doveconf | grep <some-keyword>`
+- Or: `docker exec -it <your-container-name> doveconf | grep <some-keyword>`
+
+!!! note
+    [`setup.sh`][github-file-setupsh] is included in the `docker-mailserver` repository.
+
+The `config/dovecot.cf` is copied internally to `/etc/dovecot/local.conf`. To check this file run:
+
+```sh
+docker exec -it <your-container-name> cat /etc/dovecot/local.conf
+```
+
+[github-file-setupsh]: https://github.com/docker-mailserver/docker-mailserver/blob/master/setup.sh

docs/content/config/advanced/override-defaults/postfix.md

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+---
+title: 'Override the Default Configs | Postfix'
+---
+
+The Postfix default configuration can easily be extended by providing a `config/postfix-main.cf` in postfix format.
+This can also be used to add configuration that is not in our default configuration.
+
+For example, one common use of this file is for increasing the default maximum message size:
+
+```cf
+# increase maximum message size
+message_size_limit = 52428800
+```
+
+That specific example is now supported and can be handled by setting `POSTFIX_MESSAGE_SIZE_LIMIT`.
+
+[Postfix documentation](http://www.postfix.org/documentation.html) remains the best place to find configuration options.
+
+Each line in the provided file will be loaded into postfix.
+
+In the same way it is possible to add a custom `config/postfix-master.cf` file that will override the standard `master.cf`. Each line in the file will be passed to `postconf -P`. The expected format is `<service_name>/<type>/<parameter>`, for example:
+
+```cf
+submission/inet/smtpd_reject_unlisted_recipient=no
+```
+
+Run `postconf -P` in the container without arguments to see the active master options.
+
+!!! note
+    There should be no space between the parameter and the value.
+
+Have a look at the code for more information.