Phase 5: full outbound Postfix relay (465/587 SASL+TLS, sender binding, milters)
Generate the relay config from the environment at container start (build/postfix-config.sh, run from entrypoint.sh): - smtps 465 (implicit TLS) primary + optional submission 587 (STARTTLS), chroot=n so smtpd reaches the sasldb2/sender map under /data. - Cyrus SASL against the panel-maintained sasldb2; realm left implicit so the authenticated name equals the bare login in smtpd_sender_login_maps. - reject_sender_login_mismatch + relay/recipient restrictions with no permit_mynetworks: credentials-only, open relay impossible (spec 5, 5.1). - TLS cert/key from TLS_CERT_FILE/TLS_KEY_FILE; daily postfix reload picks up renewed certs (postfix-cert-reload.sh under supervisord, spec 5.2). - anvil level-1 rate limit from env (spec 5 p.5). - Milter chain with per-milter action: OpenDKIM strict (tempfail), journal fail-open (accept) so monitoring never blocks the relay (spec 7.3). Two integration fixes found on the server: - postconf -F '*/*/chroot=n': Debian's chrooted delivery agent can't read /etc/resolv.conf, so MX lookups failed and mail never left. - entrypoint sets /run/opendkim and /run/selfpost to group selfpost + setgid, and the journal stub chmods its socket 0660, so postfix can connect to both milter sockets (strict OpenDKIM was milter-rejecting all mail otherwise). Verified on selfpost.mixfed.ru: gofmt/vet/test green, image builds; container e2e — 465 auth+send DKIM-signed (d=domain,s=selfpost), 587 STARTTLS auth, cross-domain sender 553, list-mode per-address binding, unauth relay 554, real outbound delivery reaching the recipient MX over TLS. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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#!/bin/sh
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# Generate the outbound-relay Postfix configuration (spec 5, 5.1, 5.2).
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#
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# Run as root from entrypoint.sh on every container start, BEFORE supervisord
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# starts the Postfix wrapper. Like the rest of SelfPost's runtime state it is
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# re-derived from the environment on each start rather than persisted, so a
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# fresh, restarted or restored container always ends up with the same config
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# (the only panel-edited Postfix file, sender_login_maps, lives under /data and
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# is generated separately by the panel — spec 5.1).
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#
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# main.cf is written with `postconf -e`, the master.cf submission services with
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# `postconf -M`/`-P`. No user input is interpolated: every value here comes from
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# a fixed literal or a container environment variable (spec 7.6.3).
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set -eu
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# --- environment knobs (spec 8) ----------------------------------------------
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# Server hostname: used as HELO name AND, crucially, as the Cyrus SASL realm the
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# sasldb2 accounts are looked up under. The panel creates accounts under realm
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# $SELFPOST_HOSTNAME (SASL_REALM), so myhostname MUST match or authentication
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# fails. Fall back to the container hostname only outside a real deployment.
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HOSTNAME_VALUE="${SELFPOST_HOSTNAME:-$(hostname -f 2>/dev/null || hostname)}"
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# TLS material supplied by the reverse-proxy through a read-only bind mount
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# (spec 5.2). The relay requires TLS on 465; if these files are absent the
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# master still starts but TLS handshakes on 465 fail until they appear.
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TLS_CERT="${TLS_CERT_FILE:-/etc/postfix/tls/fullchain.pem}"
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TLS_KEY="${TLS_KEY_FILE:-/etc/postfix/tls/privkey.pem}"
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# Level-1 rate limit (native Postfix anvil, spec 5 p.5 / 7.4). Conservative
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# defaults, sensible during IP warm-up (spec 10).
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RATE_MSGS="${RATE_LIMIT_MESSAGES_PER_IP:-100}"
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RATE_WINDOW="${RATE_LIMIT_WINDOW_SECONDS:-3600}"
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# Milter sockets: OpenDKIM (signing, strict) and the panel journal-milter
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# (monitoring, fail-open). Fixed container paths, matched by postfix-wrapper.sh.
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OPENDKIM_SOCK="${OPENDKIM_SOCKET:-/run/opendkim/opendkim.sock}"
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JOURNAL_SOCK="${JOURNAL_MILTER_SOCKET:-/run/selfpost/journal.sock}"
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# Persistent panel-managed sender map (spec 5.1); texthash needs no postmap, so
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# the unprivileged panel can rewrite it and just ask for a reload.
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SENDER_LOGIN_MAPS="${POSTFIX_SENDER_LOGIN_MAPS:-/data/postfix/sender_login_maps}"
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SASLDB_PATH="${SASL_DB_PATH:-/data/sasl/sasldb2}"
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# Optional submission service on 587 (spec 5 p.1: off by default, enabled only
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# when a client library needs STARTTLS on 587 instead of implicit TLS on 465).
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SUBMISSION_ENABLE="${SUBMISSION_ENABLE:-false}"
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# --- main.cf -----------------------------------------------------------------
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postconf -e \
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"myhostname=${HOSTNAME_VALUE}" \
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"maillog_file=/var/log/mail.log" \
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"mydestination=" \
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"relayhost=" \
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"inet_interfaces=all" \
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"inet_protocols=all"
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# This is an outbound relay: no local delivery, no per-user aliases. Empty
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# these so a misfiled recipient never gets delivered locally.
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postconf -e \
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"local_recipient_maps=" \
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"alias_maps=" \
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"alias_database="
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# Outbound delivery: straight to the recipient MX, opportunistic TLS (spec 5 p.2).
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postconf -e \
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"smtp_tls_security_level=may" \
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"smtp_tls_note_starttls_offer=yes"
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# TLS server material shared by every inbound service (spec 5.2). auth_only
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# guarantees credentials are never accepted before TLS is up on any port.
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postconf -e \
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"smtpd_tls_cert_file=${TLS_CERT}" \
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"smtpd_tls_key_file=${TLS_KEY}" \
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"smtpd_tls_security_level=may" \
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"smtpd_tls_auth_only=yes" \
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"smtpd_tls_loglevel=1"
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# SASL: Cyrus with the local sasldb2 the panel maintains (spec 5.1). The realm
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# is left implicit (smtpd_sasl_local_domain empty) so the authenticated name
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# Postfix uses for sender_login_maps is the BARE login the panel writes into the
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# map; the sasldb2 lookup still resolves because Postfix hands Cyrus $myhostname
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# as the server realm, which equals the realm the accounts were created under.
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postconf -e \
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"smtpd_sasl_auth_enable=yes" \
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"smtpd_sasl_type=cyrus" \
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"smtpd_sasl_path=smtpd" \
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"smtpd_sasl_local_domain=" \
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"smtpd_sasl_security_options=noanonymous" \
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"smtpd_sasl_tls_security_options=noanonymous" \
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"broken_sasl_auth_clients=yes"
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# Sender binding (spec 5.1 p.3, the critical anti-spoofing control). texthash
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# resolves the full address first, then the "@domain" wildcard, so both address
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# modes work from the same map.
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postconf -e \
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"smtpd_sender_login_maps=texthash:${SENDER_LOGIN_MAPS}"
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# Restrictions: authenticated clients only, no relay to foreign destinations,
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# and every authenticated sender address must be owned by its login. NO
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# permit_mynetworks anywhere — authorisation is by credentials, never by network
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# (spec 5 p.1/p.4, 5.1). This is what makes an open relay impossible.
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postconf -e \
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"smtpd_helo_required=yes" \
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"smtpd_relay_restrictions=permit_sasl_authenticated, reject_unauth_destination" \
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"smtpd_recipient_restrictions=permit_sasl_authenticated, reject_unauth_destination" \
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"smtpd_sender_restrictions=reject_sender_login_mismatch, permit"
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# Level-1 rate limit by client IP (spec 5 p.5). Backstop that keeps working even
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# if the journal-milter (level 2, Phase 8) is down.
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postconf -e \
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"smtpd_client_message_rate_limit=${RATE_MSGS}" \
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"anvil_rate_time_unit=${RATE_WINDOW}s"
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# Milter chain (spec 5 p.3, 7.3). OpenDKIM signs and is treated strictly
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# (default_action=tempfail: if it is unreachable, defer rather than send
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# unsigned). The journal-milter is monitoring only and is fail-open
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# (default_action=accept): its failure must never block the relay. Per-milter
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# settings use Postfix 3.0+ brace syntax.
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postconf -e \
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"milter_protocol=6" \
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"milter_default_action=tempfail" \
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"smtpd_milters={ unix:${OPENDKIM_SOCK}, default_action=tempfail }, { unix:${JOURNAL_SOCK}, default_action=accept }" \
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"non_smtpd_milters="
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# --- master.cf: inbound submission services ----------------------------------
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# smtps (465, implicit/wrapper TLS) — the primary, always-on submission service
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# (spec 5 p.1). chroot=n so smtpd can read the sasldb2 and sender map under /data
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# and the Cyrus config outside any chroot.
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postconf -M "smtps/inet=smtps inet n - n - - smtpd"
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postconf -P \
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"smtps/inet/smtpd_tls_wrappermode=yes" \
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"smtps/inet/smtpd_sasl_auth_enable=yes" \
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"smtps/inet/smtpd_client_restrictions=permit_sasl_authenticated,reject"
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# submission (587, STARTTLS) — optional (spec 5 p.1). Same SASL/milter/limits;
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# the only difference is TLS is negotiated via STARTTLS, so require encryption
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# before auth. Added only when SUBMISSION_ENABLE=true, otherwise removed so a
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# restart after disabling it does not leave the port listening.
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if [ "${SUBMISSION_ENABLE}" = "true" ]; then
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postconf -M "submission/inet=submission inet n - n - - smtpd"
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postconf -P \
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"submission/inet/smtpd_tls_security_level=encrypt" \
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"submission/inet/smtpd_sasl_auth_enable=yes" \
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"submission/inet/smtpd_client_restrictions=permit_sasl_authenticated,reject"
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else
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postconf -MX "submission/inet" 2>/dev/null || true
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fi
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# Disable chroot for every service (spec 5 p.2). Debian ships the smtp delivery
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# agent and others chrooted to /var/spool/postfix, where they cannot read
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# /etc/resolv.conf — so outbound MX lookups fail with "Host not found" and mail
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# never leaves. Inside a container the chroot buys little (the container is the
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# isolation boundary) and breaks DNS/TLS trust-store access, so turn it off
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# uniformly. Our own smtps/submission services are already n; this covers the
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# delivery agents and the rest.
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postconf -F "*/*/chroot=n"
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# --- Cyrus SASL app config for smtpd -----------------------------------------
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# Tells the Cyrus library (invoked by smtpd via smtpd_sasl_path=smtpd) to verify
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# passwords straight from the panel-maintained sasldb2 (spec 5.1). PLAIN/LOGIN
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# only — both are safe because TLS is mandatory before auth on every port.
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mkdir -p /etc/postfix/sasl
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cat > /etc/postfix/sasl/smtpd.conf <<EOF
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pwcheck_method: auxprop
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auxprop_plugin: sasldb
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sasldb_path: ${SASLDB_PATH}
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mech_list: PLAIN LOGIN
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EOF
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# Validate the generated configuration; fail loudly if postconf produced
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# anything Postfix rejects, before the wrapper tries to start it.
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postfix check
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