Add send_only_mailserver role and deploy Send-Only-Mailserver with it

Co-authored-by: yuri <yuri@nekover.se>

playbooks/roles/send_only_mail_server/README.md

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+# Role `send_only_mail_server`
+
+Makes sure a send-only mail server is deployed using OpenSMTPD and Rspamd for DKIM signing.
+
+Make sure to manually set a DMARC record and MX record for the mail domains.
+
+## Supported Distributions
+
+The following distributions are supported:
+
+- Debian 11
+
+## Required Arguments
+
+For the required arguments look at the [`argument_specs.yaml`](./meta/argument_specs.yml)
+
+Also make sure to set the following for the `cert` role dependency:
+
+- `cert__acme_account_email`
+
+## Updates
+
+This role doesn't handle updates.
+However it uses the system package manager for installing all the packages, so when you're making sure the system packages are up-to-date, you're handling updates for the packages installed by this role as well.
+
+## `hosts`
+
+The `hosts` for this role need to be the machines on which you want to deploy a mail server.
+
+## Links & Resources
+
+- <https://www.opensmtpd.org/>
+- <https://www.opensmtpd.org/manual.html>
+- <https://www.rspamd.com/>
+- <https://poolp.org/posts/2019-09-14/setting-up-a-mail-server-with-opensmtpd-dovecot-and-rspamd/>

playbooks/roles/send_only_mail_server/files/etc_rspamd_settings.conf

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+dkim_signing {
+    id = "dkim_signing";
+    apply {
+        symbols_enabled = ["DKIM_SIGNED"];
+        flags = ["skip_process"]; # Disable expensive MIME processing
+    }
+}

playbooks/roles/send_only_mail_server/handlers/main.yaml

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+- name: Restart `opensmtpd.service`
+  ansible.builtin.systemd:
+    name: opensmtpd.service
+    state: restarted
+  become: true
+
+- name: Restart `rspamd.service`
+  ansible.builtin.systemd:
+    name: rspamd.service
+    state: restarted
+  become: true

playbooks/roles/send_only_mail_server/meta/argument_specs.yaml

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+argument_specs:
+  main:
+    options:
+      send_only_mail_server__mail_server_fqdn:
+        description: The FQDN of the mail server host itself.
+        type: str
+        required: true
+      send_only_mail_server__mail_server_fqdn_zone:
+        description: >
+          The DNS zone on the BIND 9 server for records for the mail server host
+          FQDN.
+        type: str
+        required: true
+      send_only_mail_server__mail_domains:
+        description: The domains the mail server should send mails for.
+        type: list
+        elements: dict
+        required: true
+        options:
+          name:
+            description: The domain name.
+            type: str
+            required: true
+          zone:
+            description: The DNS zone on the BIND 9 server.
+            type: str
+            required: true
+      send_only_mail_server__bind_9_host:
+        description: The machine running BIND 9 to deploy DNS records via.
+        type: str
+        required: true

playbooks/roles/send_only_mail_server/meta/main.yaml

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+dependencies: # noqa meta-no-info
+  - role: distribution_check
+    vars:
+      distribution_check__supported_distributions:
+        - name: Debian
+          versions:
+            - "11"

playbooks/roles/send_only_mail_server/tasks/ensure_dkim_keypair.yaml

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+- name: make sure DKIM private key exists
+  community.crypto.openssl_privatekey:
+    path: "/etc/mail-dkim/{{ item.name }}.key"
+    size: 1024
+    type: RSA
+    owner: "root"
+    group: "_rspamd"
+    mode: "0640"
+  become: true
+  notify: Restart `rspamd.service`
+
+- name: make sure DKIM public key exists
+  community.crypto.openssl_publickey:
+    path: "/etc/mail-dkim/{{ item.name }}.pub"
+    privatekey_path: "/etc/mail-dkim/{{ item.name }}.key"
+    return_content: true
+  become: true
+  notify: Restart `rspamd.service`
+  register: send_only_mail_server__dkim_public_key
+
+- name: deploy DKIM public key DNS entry  # noqa: no-handler
+  delegate_to: "{{ send_only_mail_server__bind_9_host }}"
+  when: send_only_mail_server__dkim_public_key.changed
+  block:
+    - name: Add file containing nsupdate commands for removing DKIM public key TXT records
+      ansible.builtin.template:
+        src: nsupdate_delete_dkim_public_key_txt_records.j2
+        dest: /root/nsupdate_delete_dkim_public_key_txt_records
+        owner: root
+        group: root
+        mode: "0600"
+
+    - name: Remove DNS records from BIND 9 server via nsupdate  # noqa: no-changed-when
+      ansible.builtin.command: /usr/bin/nsupdate -l /root/nsupdate_delete_dkim_public_key_txt_records
+
+    - name: Add file containing nsupdate commands for adding DKIM public key TXT record
+      ansible.builtin.template:
+        src: nsupdate_add_dkim_public_key_txt_record.j2
+        dest: /root/nsupdate_add_dkim_public_key_txt_record
+        owner: root
+        group: root
+        mode: "0600"
+
+    - name: Add DNS record to BIND 9 server via nsupdate  # noqa: no-changed-when
+      ansible.builtin.command: /usr/bin/nsupdate -l /root/nsupdate_add_dkim_public_key_txt_record
+  always:
+    - name: Remove file containing nsupdate commands for removing DKIM public key TXT records again
+      ansible.builtin.file:
+        path: /root/nsupdate_delete_dkim_public_key_txt_records
+        state: absent
+
+    - name: Remove file containing nsupdate commands for adding DKIM public key TXT record again
+      ansible.builtin.file:
+        path: /root/nsupdate_add_dkim_public_key_txt_record
+        state: absent

playbooks/roles/send_only_mail_server/tasks/main.yaml

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+- name: make sure packages are installed
+  ansible.builtin.apt:
+    name:
+      - opensmtpd
+      - rspamd
+      - opensmtpd-filter-rspamd
+  become: true
+
+- name: make sure certificates exist
+  ansible.builtin.include_role:
+    name: cert
+  vars:
+    cert__domains:
+      - "{{ send_only_mail_server__mail_server_fqdn }}"
+    cert__owner: root
+    cert__group: opensmtpd
+    cert__bind_9_zone: "{{ send_only_mail_server__mail_server_fqdn_zone }}"
+    cert__bind_9_host: "{{ send_only_mail_server__bind_9_host }}"
+    cert__privkey_pem_permissions: "0640"
+    cert__fullchain_pem_permissions: "0640"
+    cert__chain_pem_permissions: "0640"
+    cert__cert_pem_permissions: "0640"
+
+- name: make sure the OpenSMTPD config is deployed
+  ansible.builtin.template:
+    src: etc_smtpd.conf.j2
+    dest: /etc/smtpd.conf
+    owner: root
+    group: root
+    mode: "0600"
+  become: true
+  notify: Restart `opensmtpd.service`
+
+- name: make sure `/etc/mail-dkim` directory exists
+  ansible.builtin.file:
+    path: /etc/mail-dkim
+    state: directory
+    owner: root
+    group: root
+    mode: "755"
+  become: true
+
+- name: make sure DKIM keypairs for all domains exist
+  loop: "{{ send_only_mail_server__mail_domains }}"
+  ansible.builtin.include_tasks: ensure_dkim_keypair.yaml
+
+- name: make sure the Rspamd `dkim_signing.conf` is deployed
+  ansible.builtin.template:
+    src: etc_rspamd_dkim_signing.conf.j2
+    dest: /etc/rspamd/local.d/dkim_signing.conf
+    owner: root
+    group: root
+    mode: "0600"
+  become: true
+  notify: Restart `rspamd.service`
+
+- name: make sure the Rspamd `settings.conf` is deployed
+  ansible.builtin.copy:
+    src: etc_rspamd_settings.conf
+    dest: /etc/rspamd/local.d/settings.conf
+    owner: root
+    group: root
+    mode: "0600"
+  become: true
+  notify: Restart `rspamd.service`

playbooks/roles/send_only_mail_server/templates/etc_rspamd_dkim_signing.conf.j2

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+allow_username_mismatch = true;
+
+use_esld = false;
+
+domain {
+{% for mail_domain in send_only_mail_server__mail_domains %}
+    {{ mail_domain.name }} {
+        path = "/etc/mail-dkim/{{ mail_domain.name }}.key";
+        selector = "key";
+    }
+{% endfor %}
+}

playbooks/roles/send_only_mail_server/templates/etc_smtpd.conf.j2

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+# Managed by Ansible.
+# This configuration enables sending emails using this server, but to not receiving any.
+
+pki {{ send_only_mail_server__mail_server_fqdn }} cert "/etc/ansible_certs/certs/{{ send_only_mail_server__mail_server_fqdn }}/fullchain.pem"
+pki {{ send_only_mail_server__mail_server_fqdn }} key "/etc/ansible_certs/certs/{{ send_only_mail_server__mail_server_fqdn }}/privkey.pem"
+
+filter "rspamd-dkim-signing" proc-exec "filter-rspamd -settings-id dkim_signing"
+
+listen on lo
+listen on eth0 smtps pki {{ send_only_mail_server__mail_server_fqdn }} auth filter "rspamd-dkim-signing"
+listen on eth0 tls-require pki {{ send_only_mail_server__mail_server_fqdn }} auth filter "rspamd-dkim-signing"
+
+action "outbound" relay helo {{ send_only_mail_server__mail_server_fqdn }}
+
+match from any auth for any action "outbound"

playbooks/roles/send_only_mail_server/templates/nsupdate_add_dkim_public_key_txt_record.j2

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+debug
+zone {{ item.zone }}
+update add key._domainkey.{{ item.name }} 60 TXT v=DKIM1;k=rsa;p={{ send_only_mail_server__dkim_public_key.publickey | replace('\n', '') | replace('-----BEGIN PUBLIC KEY-----', '') | replace('-----END PUBLIC KEY-----', '') }}
+send

playbooks/roles/send_only_mail_server/templates/nsupdate_delete_dkim_public_key_txt_records.j2

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+debug
+zone {{ item.zone }}
+update delete key._domainkey.{{ item.name }} TXT
+send