Из коробки, rspamd не умеет делать экспорт в формате prometheus.

Для реализации цели будем использовать graphite-exporter.

Сторона graphite-exporter:

mappings:
- match: rspamd.actions.*
  name: rspamd_actions
  labels:
    action: $1

Сторона rspamd в файле metric_exporter.conf:

backend = "graphite";
host = "graphite-exporter";
port = 9109;
timeout = 10;
interval = 60;

metrics = [
    "actions.add header",
    "actions.greylist",
    "actions.no action",
    "actions.reject",
    "actions.rewrite subject",
    "actions.soft reject",
    "bytes_allocated",
    "chunks_allocated",
    "chunks_freed",
    "chunks_oversized",
    "connections",
    "control_connections",
    "ham_count",
    "learned",
    "pools_allocated",
    "pools_freed",
    "scanned",
    "shared_chunks_allocated",
    "spam_count"
];

Сторона prometheus:

- job_name: 'graphite-exporter'
  scrape_interval: 30s
  static_configs:
  - targets: ["graphite-exporter:9108"]

Дальше на средствах визуализациях можно отображать собранные данные.