Caddy will print out config errors to the logs when it fails to start up. See this page in the docs to see how to use Caddy as a service, including the right command to see the logs:
In this case, you have more opening { than closing } so the Caddyfile adapter isn’t happy.
I think this might be what you’re looking for:
mail.example.com {
reverse_proxy https://192.168.1.230:443 {
transport http {
tls_insecure_skip_verify
}
}
}
You don’t need to specify tls if you used https:// on the upstream address.
Keep in mind that using tls_insecure_skip_verify turns off all security offered by using HTTPS/TLS when proxying, it’s effectively the same as using HTTP in terms of security, but with extra encryption overhead.