feat(postfix-pgsql): add Dockerfile with templated config and entrypoint

images/postfix-pgsql/templates/main.cf.template

@@ -0,0 +1,39 @@
+# =============================================================================
+# Postfix main.cf template
+#
+# Rendered at container startup by docker-entrypoint.sh, with values
+# substituted from environment variables. See README.md for the full list
+# of supported variables.
+# =============================================================================
+
+myhostname = ${MYHOSTNAME}
+mydomain = ${MAIL_DOMAIN}
+myorigin = $mydomain
+mydestination =
+inet_interfaces = all
+inet_protocols = ipv4
+
+# Dynamic relay/transport decisions backed by PostgreSQL lookup maps.
+relay_domains = pgsql:/etc/postfix/pgsql-relay-domains.cf
+transport_maps = pgsql:/etc/postfix/pgsql-transport-maps.cf
+
+# This instance only relays mail for the domains returned by relay_domains;
+# it does not accept mail for arbitrary destinations.
+smtpd_relay_restrictions = permit_mynetworks, reject_unauth_destination
+mynetworks = 127.0.0.0/8, [::1]/128
+
+# TLS
+smtpd_tls_cert_file = ${SMTPD_TLS_CERT_FILE}
+smtpd_tls_key_file = ${SMTPD_TLS_KEY_FILE}
+smtpd_use_tls = yes
+smtpd_tls_security_level = may
+smtp_tls_security_level = may
+
+# Log to stdout/stderr so `docker logs` captures Postfix activity directly,
+# without needing a syslog daemon inside the container.
+maillog_file = /dev/stdout
+
+biff = no
+append_dot_mydomain = no
+readme_directory = no
+compatibility_level = 3.6

images/postfix-pgsql/templates/pgsql-relay-domains.cf.template

@@ -0,0 +1,12 @@
+# =============================================================================
+# Postfix pgsql_table lookup: relay_domains
+#
+# Returns the domain itself when Postfix should relay mail for it.
+# Rendered at container startup from environment variables.
+# =============================================================================
+
+user = ${POSTGRES_USER}
+password = ${POSTGRES_PASSWORD}
+hosts = ${POSTGRES_HOST}:${POSTGRES_PORT}
+dbname = ${POSTGRES_DB}
+query = SELECT domain FROM relay_domain WHERE domain='%s'

images/postfix-pgsql/templates/pgsql-transport-maps.cf.template

@@ -0,0 +1,15 @@
+# =============================================================================
+# Postfix pgsql_table lookup: transport_maps
+#
+# Returns the internal SMTP relay target that accepted mail gets forwarded
+# to once a recipient domain matches relay_domains. The target itself is
+# baked into the query from SMTP_RELAY_HOST/SMTP_RELAY_PORT at startup; this
+# image has no further knowledge of what consumes the mail downstream.
+# Rendered at container startup from environment variables.
+# =============================================================================
+
+user = ${POSTGRES_USER}
+password = ${POSTGRES_PASSWORD}
+hosts = ${POSTGRES_HOST}:${POSTGRES_PORT}
+dbname = ${POSTGRES_DB}
+query = SELECT 'smtp:[${SMTP_RELAY_HOST}]:${SMTP_RELAY_PORT}' FROM relay_domain WHERE domain='%s'