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

images/postfix-pgsql/Dockerfile

@@ -0,0 +1,38 @@
+# =============================================================================
+# Postfix + PostgreSQL Relay/MTA Image
+#
+# A pure SMTP relay/MTA: receives inbound mail and forwards it based on
+# PostgreSQL-backed relay_domains/transport_maps lookups, equivalent to the
+# Postfix setup described in the SimpleLogin self-hosting documentation
+# (https://github.com/simple-login/app). No domain, hostname, or database
+# credentials are baked into the image; everything is templated from
+# environment variables at container startup. This image has no knowledge
+# of what consumes the relayed mail.
+# =============================================================================
+
+# POSTFIX_VERSION pins the Debian base image tag (e.g. "12-slim"), which in
+# turn pins the postfix/postfix-pgsql package versions available via apt.
+ARG POSTFIX_VERSION=12-slim
+FROM debian:${POSTFIX_VERSION}
+
+LABEL maintainer="Damien Arnodo"
+LABEL description="Postfix SMTP relay/MTA with PostgreSQL-backed relay_domains and transport_maps lookups"
+
+RUN echo "postfix postfix/main_mailer_type select No configuration" | debconf-set-selections \
+    && echo "postfix postfix/mailname string localhost" | debconf-set-selections \
+    && apt-get update \
+    && apt-get install -y --no-install-recommends \
+        postfix \
+        postfix-pgsql \
+        gettext-base \
+        openssl \
+        ca-certificates \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY templates/ /etc/postfix/templates/
+COPY docker-entrypoint.sh /usr/local/bin/docker-entrypoint.sh
+RUN chmod +x /usr/local/bin/docker-entrypoint.sh
+
+EXPOSE 25
+
+ENTRYPOINT ["docker-entrypoint.sh"]