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