Recategorize Postmoogle (#3696)

* Update configuring-playbook.md: move a link for docs/configuring-playbook-bot-postmoogle.md to Bots section

The document (on 9c2a8addee93910cb9079f856bc3fb3932592c91; initial commit to add Postmoogle) says:
> Postmoogle is a bot/bridge you can use to forward emails to Matrix rooms

Therefore it is not really incorrect to categorize Postmoogle as bridge document-wise, but since the list on README.md categorizes it as a bot, and based on the file name of the documentation, this commit moves the link for Postmoogle to the Bots section.

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Revert "Update configuring-playbook.md: move a link for docs/configuring-playbook-bot-postmoogle.md to Bots section"

This reverts commit 1e2e903cb9.

* Change the file name of Postmoogle documentation to make it clear that Postmoogle is a bridge

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update documentation for Postmoogle related to a bridge/bot status

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

---------

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>
Co-authored-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

docs/configuring-playbook-bridge-postmoogle.md

@@ -0,0 +1,83 @@
+# Setting up Postmoogle email bridging (optional)
+
+**Note**: email bridging can also happen via the [email2matrix](configuring-playbook-email2matrix.md) bridge supported by the playbook.
+
+The playbook can install and configure [Postmoogle](https://github.com/etkecc/postmoogle) for you.
+
+Postmoogle is a bridge you can use to have its bot user forward emails to Matrix rooms. It runs an SMTP email server and allows you to assign mailbox addresses to the rooms.
+
+See the project's [documentation](https://github.com/etkecc/postmoogle) to learn what it does and why it might be useful to you.
+
+## Prerequisites
+
+Open the following ports on your server to be able to receive incoming emails:
+
+  - `25/tcp`: SMTP
+  - `587/tcp`: Submission (TLS-encrypted SMTP)
+
+If you don't open these ports, you will still be able to send emails, but not receive any.
+
+These port numbers are configurable via the `matrix_bot_postmoogle_smtp_host_bind_port` and `matrix_bot_postmoogle_submission_host_bind_port` variables, but other email servers will try to deliver on these default (standard) ports, so changing them is of little use.
+
+
+## Adjusting the playbook configuration
+
+Add the following configuration to your `inventory/host_vars/matrix.example.com/vars.yml` file:
+
+```yaml
+matrix_bot_postmoogle_enabled: true
+
+# Uncomment and adjust this part if you'd like to use a username different than the default
+# matrix_bot_postmoogle_login: postmoogle
+
+# Generate a strong password here. Consider generating it with `pwgen -s 64 1`
+matrix_bot_postmoogle_password: PASSWORD_FOR_THE_BOT
+
+# Uncomment to add one or more admins to this bridge:
+#
+# matrix_bot_postmoogle_admins:
+#  - '@yourAdminAccount:{{ matrix_domain }}'
+#
+# .. unless you've made yourself an admin of all bots/bridges like this:
+#
+# matrix_admin: '@yourAdminAccount:{{ matrix_domain }}'
+```
+
+## Adjusting DNS records
+
+You will also need to add several DNS records so that Postmoogle can send emails. See [Configuring DNS](configuring-dns.md) for details about DNS changes.
+
+## Installing
+
+After configuring the playbook, run the [installation](installing.md) command:
+
+```sh
+ansible-playbook -i inventory/hosts setup.yml --tags=setup-all,ensure-matrix-users-created,start
+```
+
+**Notes**:
+
+- the `ensure-matrix-users-created` playbook tag makes the playbook automatically create a user account of the bridge's bot
+
+- if you change the bridge's bot password (`matrix_bot_postmoogle_password` in your `vars.yml` file) subsequently, the bot user's credentials on the homeserver won't be updated automatically. If you'd like to change the bot user's password, use a tool like [synapse-admin](configuring-playbook-synapse-admin.md) to change it, and then update `matrix_bot_postmoogle_password` to let the bot know its new password
+
+
+## Usage
+
+To use the bridge, invite the `@postmoogle:example.com` bot user into a room you want to use as a mailbox.
+
+Then send `!pm mailbox NAME` to expose this Matrix room as an inbox with the email address `NAME@matrix.example.com`. Emails sent to that email address will be forwarded to the room.
+
+Send `!pm help` to the room to see the bridge's help menu for additional commands.
+
+You can also refer to the upstream [documentation](https://github.com/etkecc/postmoogle).
+
+### Debug/Logs
+
+As with all other services, you can find their logs in [systemd-journald](https://www.freedesktop.org/software/systemd/man/systemd-journald.service.html) by running something like `journalctl -fu matrix-bot-postmoogle`
+
+The default logging level for this bridge is `INFO`, but you can increase it to `DEBUG` with the following additional configuration:
+
+```yaml
+matrix_bot_postmoogle_loglevel: 'DEBUG'
+```