Dedicated Listener for Prometheus Metrics Endpoint

Stalwart already exposes Prometheus metrics, which makes monitoring integrations very straightforward.

Currently, when Prometheus metrics are enabled, the metrics endpoint becomes available on every HTTP-enabled listener. In environments with multiple http listeners, this can unintentionally expose metrics more broadly than desired.

It would be great to have a dedicated configuration option for metrics exposure by allowing administrators to bind metrics to a specific listener.

This would also align well with how many modern services separate application traffic from observability endpoints.

Example idea:

  1. Create a new listener called metrics → or use an existing one

  2. Configure Prometheus listener (see new option “Listener”)