mail_relay: postfix relays all mail through the mailcow submission port with a mailbox per host, replaces mail_aliases

mail_relay/defaults/main.yml

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+---
+# Every host sends its mail through the mailcow submission port with its own mailbox
+# (doc/host-mail-relay.md in the kubernetes repo). The password is set in host_vars.
+mail_relay:
+  host: tranio.ruekov.eu
+  port: 587
+  # SASL login of the mailcow mailbox; the password is an SMTP-only app password of it.
+  username: "{{ inventory_hostname_short }}.system@mail.ruekov.eu"
+  # Sender address every local address is rewritten to; mailcow accepts only addresses of the login.
+  sender: "{{ mail_relay.username }}"
+  password: ""
+  # Root mail goes to this address: /etc/aliases and, on Proxmox hosts, the email of root@pam.
+  root_mail: admin@ruekov.eu
+  myhostname: "{{ inventory_hostname }}"
+  # The local postfix only takes mail from the host itself.
+  inet_interfaces: loopback-only
+  # The smtp inet service of master.cf; off where another daemon holds port 25 (tranio: mailcow).
+  smtpd_listener: true

mail_relay/handlers/main.yml

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+---
+- name: Restart postfix
+  ansible.builtin.service:
+    name: postfix
+    state: restarted

mail_relay/tasks/main.yml

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+---
+- name: Mailbox password is set
+  ansible.builtin.assert:
+    that: mail_relay.password | length > 0
+    fail_msg: "mail_relay.password of {{ inventory_hostname }} is empty (host_vars)"
+    quiet: true
+
+- name: Postfix state
+  ansible.builtin.stat:
+    path: /usr/sbin/postfix
+  register: mail_relay_postfix
+
+- name: Exim state
+  ansible.builtin.stat:
+    path: /usr/sbin/exim4
+  register: mail_relay_exim
+
+# Postfix replaces exim4 as the mail-transport-agent; the package scripts do not stop a running exim4
+# while policy-rc.d denies service actions, and its listener would block postfix on port 25.
+- name: Stop exim4
+  ansible.builtin.systemd_service:
+    name: exim4
+    state: stopped
+    enabled: false
+  when: mail_relay_exim.stat.exists and not mail_relay_postfix.stat.exists
+
+- name: Preseed postfix
+  ansible.builtin.debconf:
+    name: postfix
+    question: "{{ item.question }}"
+    vtype: "{{ item.vtype }}"
+    value: "{{ item.value }}"
+  loop:
+    - { question: postfix/main_mailer_type, vtype: select, value: Internet Site }
+    - { question: postfix/mailname, vtype: string, value: "{{ mail_relay.myhostname }}" }
+  loop_control:
+    label: "{{ item.question }}"
+  when: not mail_relay_postfix.stat.exists
+
+# A third-party repository with a bad signature makes the refresh fail on some hosts; the install
+# below still fails if the index lacks the packages.
+- name: Refresh apt cache
+  ansible.builtin.apt:
+    update_cache: true
+    cache_valid_time: 3600
+  failed_when: false
+
+# The package starts postfix with the Debian defaults, which listen on all interfaces; on a host whose
+# port 25 is taken (tranio: mailcow) that start fails. policy-rc.d keeps the start until the
+# configuration is in place.
+- name: Install postfix
+  ansible.builtin.apt:
+    name:
+      - postfix
+      - libsasl2-modules
+      - ca-certificates
+    policy_rc_d: "{{ omit if mail_relay_postfix.stat.exists else 101 }}"
+
+- name: Postfix configuration
+  when: not ansible_check_mode or mail_relay_postfix.stat.exists
+  block:
+    - name: Local names of the host
+      ansible.builtin.set_fact:
+        mail_relay_local_names: >-
+          {{ [mail_relay.myhostname, inventory_hostname, inventory_hostname_short, ansible_facts['hostname'],
+              'localhost', 'localhost.localdomain'] | unique }}
+
+    - name: Sender rewrite map
+      ansible.builtin.template:
+        src: generic.regexp.j2
+        dest: /etc/postfix/generic
+        owner: root
+        group: root
+        mode: "0644"
+      notify: Restart postfix
+
+    - name: Relay settings in main.cf
+      ansible.builtin.lineinfile:
+        path: /etc/postfix/main.cf
+        regexp: "^{{ item.key }}\\s*="
+        line: "{{ item.key }} = {{ item.value }}"
+      loop: "{{ mail_relay_settings | dict2items }}"
+      vars:
+        mail_relay_settings:
+          myhostname: "{{ mail_relay.myhostname }}"
+          myorigin: $myhostname
+          inet_interfaces: "{{ mail_relay.inet_interfaces }}"
+          relayhost: "[{{ mail_relay.host }}]:{{ mail_relay.port }}"
+          smtp_sasl_auth_enable: "yes"
+          smtp_sasl_password_maps: hash:/etc/postfix/sasl_passwd
+          smtp_sasl_security_options: noanonymous
+          smtp_tls_security_level: verify
+          smtp_tls_CAfile: /etc/ssl/certs/ca-certificates.crt
+          smtp_generic_maps: regexp:/etc/postfix/generic
+      loop_control:
+        label: "{{ item.key }}"
+      notify: Restart postfix
+
+    - name: SASL credentials
+      ansible.builtin.copy:
+        dest: /etc/postfix/sasl_passwd
+        content: "[{{ mail_relay.host }}]:{{ mail_relay.port }} {{ mail_relay.username }}:{{ mail_relay.password }}\n"
+        owner: root
+        group: root
+        mode: "0600"
+      no_log: true
+      register: mail_relay_sasl
+
+    - name: SASL database state
+      ansible.builtin.stat:
+        path: /etc/postfix/sasl_passwd.db
+      register: mail_relay_sasl_db
+
+    # A task instead of a handler: a failed run would drop the notification and leave the database missing.
+    - name: Rebuild sasl_passwd database
+      ansible.builtin.command:
+        cmd: postmap /etc/postfix/sasl_passwd
+      when: mail_relay_sasl.changed or not mail_relay_sasl_db.stat.exists
+      changed_when: true
+      notify: Restart postfix
+
+    # inet_interfaces cannot switch the listener off ("none" is resolved as a host name): the service
+    # is commented out in master.cf instead.
+    - name: SMTP listener in master.cf
+      ansible.builtin.lineinfile:
+        path: /etc/postfix/master.cf
+        regexp: "^#?smtp\\s+inet\\s+n\\s+-\\s+y\\s+-\\s+-\\s+smtpd\\s*$"
+        line: "{{ '' if mail_relay.smtpd_listener else '#' }}smtp      inet  n       -       y       -       -       smtpd"
+      notify: Restart postfix
+
+    - name: Root alias
+      ansible.builtin.lineinfile:
+        path: /etc/aliases
+        regexp: "^root:"
+        line: "root: {{ mail_relay.root_mail }}"
+        create: true
+        owner: root
+        group: root
+        mode: "0644"
+
+    - name: Alias file state
+      ansible.builtin.stat:
+        path: /etc/aliases
+      register: mail_relay_aliases
+
+    - name: Alias database state
+      ansible.builtin.stat:
+        path: /etc/aliases.db
+      register: mail_relay_aliases_db
+
+    # Postfix reads /etc/aliases through the compiled /etc/aliases.db; without a current db local
+    # delivery defers or misroutes. A task instead of a handler, so a failed run cannot lose the rebuild.
+    - name: Rebuild alias database
+      ansible.builtin.command:
+        cmd: newaliases
+      when: >-
+        not mail_relay_aliases_db.stat.exists
+        or mail_relay_aliases_db.stat.mtime < mail_relay_aliases.stat.mtime
+      changed_when: true
+
+    - name: Apply pending changes
+      ansible.builtin.meta: flush_handlers
+
+    - name: SASL database permissions
+      ansible.builtin.file:
+        path: /etc/postfix/sasl_passwd.db
+        owner: root
+        group: root
+        mode: "0600"
+
+    - name: Postfix running
+      ansible.builtin.service:
+        name: postfix
+        state: started
+        enabled: true
+
+- name: Proxmox state
+  ansible.builtin.stat:
+    path: /usr/sbin/pveum
+  register: mail_relay_pve
+
+# The built-in mail-to-root notification target mails the email of root@pam.
+- name: Email of root@pam
+  when: mail_relay_pve.stat.exists
+  block:
+    - name: Read root@pam
+      ansible.builtin.command:
+        cmd: pvesh get /access/users/root@pam --output-format json
+      register: mail_relay_pve_root
+      changed_when: false
+      check_mode: false
+
+    - name: Set the email of root@pam
+      ansible.builtin.command:
+        cmd: "pveum user modify root@pam --email {{ mail_relay.root_mail }}"
+      when: (mail_relay_pve_root.stdout | from_json).email | default('') != mail_relay.root_mail
+
+# Run with --tags mail_relay_test: the mail takes the root alias through the relay.
+- name: Test mail to root
+  ansible.builtin.command:
+    cmd: sendmail -t
+    stdin: |
+      To: root
+      Subject: mail_relay test from {{ inventory_hostname }}
+
+      Test mail of the mail_relay role.
+  changed_when: true
+  tags: [never, mail_relay_test]

mail_relay/templates/generic.regexp.j2

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+# mailcow rejects a sender that does not belong to the login of the submission, so every address of
+# this host is rewritten to the mailbox. The map also applies to recipient addresses: only the names
+# of this host match, never a recipient such as admin@ruekov.eu.
+/^[^@]+@({{ mail_relay_local_names | map('regex_escape') | join('|') }})$/ {{ mail_relay.sender }}