thermograph/deploy/provision-mail.sh

#!/usr/bin/env bash
# Outbound email for Thermograph — run once on the VPS, as root.
#
# Installs Postfix as a SEND-ONLY NULL CLIENT: it listens on 127.0.0.1:25 only,
# accepts mail from this machine, and never receives mail from the internet.
#
# Why a local MTA instead of talking to a mail provider's API from Python:
#
#   * The app's only mail config becomes "SMTP on localhost". Whether delivery
#     then goes direct to the recipient's MX or through a relay is a Postfix
#     setting — switchable without touching, redeploying, or retesting the app.
#   * Postfix queues and retries. A request handler hands the message over in
#     microseconds and returns; a slow or briefly-down upstream can't stall a
#     web request or lose a signup.
#   * No new Python dependency: stdlib smtplib talks to it (see backend/mailer.py).
#
# DELIVERABILITY — read before pointing this at real subscribers.
#
# Mail sent straight from a VPS IP is very often junked, regardless of Postfix
# config, because the IP has no sending reputation. Two options:
#
#   A. RELAY through a transactional provider (recommended for real mail).
#      Set RELAYHOST + RELAY_USER + RELAY_PASSWORD below. The provider handles
#      SPF/DKIM alignment and reputation; you keep the loopback-SMTP seam.
#
#   B. DIRECT to MX (no third party). Then you must also set up, in DNS:
#        - SPF:   TXT @  "v=spf1 a mx ip4:<VPS_IP> -all"
#        - DKIM:  install opendkim, publish the public key as a TXT record
#        - DMARC: TXT _dmarc  "v=DMARC1; p=none; rua=mailto:you@domain"
#        - PTR / reverse DNS on the VPS IP -> mail.thermograph.org
#      The PTR record is the one people forget, and its absence alone is enough
#      for Gmail and Outlook to junk everything you send.
#
# Usage:
#   sudo MAIL_DOMAIN=thermograph.org bash deploy/provision-mail.sh
#   sudo MAIL_DOMAIN=thermograph.org RELAYHOST='[smtp.provider.com]:587' \
#        RELAY_USER=apikey RELAY_PASSWORD=secret bash deploy/provision-mail.sh
set -euo pipefail

MAIL_DOMAIN="${MAIL_DOMAIN:-thermograph.org}"
MAIL_HOSTNAME="${MAIL_HOSTNAME:-mail.${MAIL_DOMAIN}}"
RELAYHOST="${RELAYHOST:-}"
RELAY_USER="${RELAY_USER:-}"
RELAY_PASSWORD="${RELAY_PASSWORD:-}"

if [[ $EUID -ne 0 ]]; then
  echo "run as root (sudo)" >&2
  exit 1
fi

echo "==> installing postfix (non-interactive)"
export DEBIAN_FRONTEND=noninteractive
# Preseed so the installer doesn't open its curses dialog.
debconf-set-selections <<EOF
postfix postfix/main_mailer_type select Internet Site
postfix postfix/mailname string ${MAIL_HOSTNAME}
EOF
apt-get update -qq
apt-get install -y -qq postfix libsasl2-modules

echo "==> configuring send-only null client"
postconf -e "myhostname = ${MAIL_HOSTNAME}"
postconf -e "myorigin = ${MAIL_DOMAIN}"
# THE important line: never listen on a public interface. This box sends only.
postconf -e "inet_interfaces = loopback-only"
postconf -e "inet_protocols = ipv4"
# Accept mail only from this machine.
postconf -e "mynetworks = 127.0.0.0/8 [::1]/128"
# A null client delivers nothing locally; everything is relayed out.
postconf -e "mydestination ="
postconf -e "local_transport = error:local delivery is disabled"
# Use TLS opportunistically when talking to the next hop.
postconf -e "smtp_tls_security_level = may"
postconf -e "smtp_tls_loglevel = 1"

if [[ -n "$RELAYHOST" ]]; then
  echo "==> configuring relay via ${RELAYHOST}"
  postconf -e "relayhost = ${RELAYHOST}"
  if [[ -n "$RELAY_USER" ]]; then
    postconf -e "smtp_sasl_auth_enable = yes"
    postconf -e "smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd"
    postconf -e "smtp_sasl_security_options = noanonymous"
    printf '%s %s:%s\n' "$RELAYHOST" "$RELAY_USER" "$RELAY_PASSWORD" \
      > /etc/postfix/sasl_passwd
    # The credential file must not be world-readable.
    chmod 600 /etc/postfix/sasl_passwd
    postmap /etc/postfix/sasl_passwd
    chmod 600 /etc/postfix/sasl_passwd.db
  fi
else
  echo "==> no RELAYHOST set: delivering direct to MX"
  echo "    remember SPF + DKIM + DMARC + PTR, or expect the spam folder"
  postconf -e "relayhost ="
fi

systemctl enable postfix
systemctl restart postfix

echo "==> verifying it listens on loopback only"
ss -lntp | grep ':25 ' || true

cat <<'NOTE'

==> next steps

1. Point the app at it, in /etc/thermograph.env:

     THERMOGRAPH_MAIL_BACKEND=smtp
     THERMOGRAPH_SMTP_HOST=127.0.0.1
     THERMOGRAPH_SMTP_PORT=25
     THERMOGRAPH_MAIL_FROM=Thermograph <no-reply@thermograph.org>

   then: sudo systemctl restart thermograph

2. Send yourself a test message:

     echo "test body" | mail -s "thermograph test" you@example.com
     # or, exercising the app's own path:
     #   python -c "import sys; sys.path.insert(0,'/opt/thermograph/backend'); \
     #              import mailer; print(mailer.send('you@example.com','t','body'))"

3. Watch it leave:  journalctl -u postfix -f     (queue: mailq)

4. Check placement with https://www.mail-tester.com — it scores SPF, DKIM,
   DMARC and rDNS in one shot and tells you exactly what's missing.
NOTE