This update includes a few features that make it easier to work
with relay hosts. The configuration now uses built-in (Alpine) TLS
certificates and allows the user to specify how the Postfix should
establish a TLS connection. Configure it using `RELAYHOST_TLS_LEVEL`,
if needed.
Another configuration option was added, `MESSAGE_SIZE_LIMIT`, which
enables you to reject messages exceeding certain limits. Especially
useful with relay servers, to prevent messages getting stuck in
Postfix queue.
Use the `INBOUND_DEBUGGING` parameter to enable additional postfix
logs for incoming messages when things go south.
Use `TZ` parameter to set the timezone of the container (especially
useful for logs and dates in the messages).
*Notice that `ALLOWED_SENDER_DOMAINS` is now a neccessary parameter.*
Turns out that due to Postfix anti-spam configuration there's no way
to start it properly without specifying the domains it will relay
email for.
This commit also includes a few samples of running the container:
- standalone
- in [docker-compose](https://docs.docker.com/compose/)
Further work: add a working Kubernetes / Helm chart example.
