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SRMTA Monitoring & Alerting Guide

Prometheus Metrics Reference

SMTP Server

Metric Type Description
srmta_smtp_connections_total counter Total inbound connections
srmta_smtp_connections_active gauge Currently active connections
srmta_smtp_connections_rejected counter Rejected connections (rate limit, max connections)
srmta_smtp_messages_accepted_total counter Successfully accepted messages
srmta_smtp_processing_latency_seconds histogram Message processing latency
srmta_smtp_message_size_bytes histogram Message size distribution

Authentication

Metric Type Description
srmta_auth_success_total counter Successful authentications
srmta_auth_failure_total counter Failed authentication attempts

TLS

Metric Type Description
srmta_tls_connections_total counter TLS connections established
srmta_tls_handshake_errors_total counter TLS handshake failures

Queue

Metric Type Description
srmta_queue_enqueued_total counter Messages enqueued
srmta_queue_completed_total counter Messages delivered successfully
srmta_queue_deferred_total counter Messages deferred (will retry)
srmta_queue_failed_total counter Messages permanently failed
srmta_queue_dead_letter_total counter Messages moved to dead-letter
srmta_queue_processing_total counter Messages currently being processed

Delivery

Metric Type Description
srmta_delivery_success_total counter Successfully delivered messages
srmta_delivery_duration_seconds histogram End-to-end delivery time

Health Check Endpoints

Endpoint Description
GET /health Simple liveness check — returns {"status":"healthy"}
GET /health/full Detailed subsystem status (SMTP, queue, delivery, auth, TLS)
GET /metrics Prometheus exposition format metrics

Recommended Alerting Rules

groups:
  - name: srmta
    rules:
      # Queue growing — delivery may be failing
      - alert: QueueBacklog
        expr: srmta_queue_enqueued_total - srmta_queue_completed_total - srmta_queue_failed_total > 10000
        for: 15m
        labels:
          severity: warning

      # High bounce rate
      - alert: HighBounceRate
        expr: rate(srmta_bounce_total[1h]) / rate(srmta_delivery_success_total[1h]) > 0.05
        for: 30m
        labels:
          severity: critical

      # Auth brute force attempt
      - alert: AuthBruteForce
        expr: rate(srmta_auth_failure_total[5m]) > 10
        for: 5m
        labels:
          severity: warning

      # TLS errors spiking
      - alert: TLSErrors
        expr: rate(srmta_tls_handshake_errors_total[5m]) > 5
        for: 10m
        labels:
          severity: warning

      # No deliveries happening
      - alert: NoDeliveries
        expr: rate(srmta_delivery_success_total[15m]) == 0
        for: 30m
        labels:
          severity: critical

      # Connections being rejected (rate limiting)
      - alert: ConnectionsRejected
        expr: rate(srmta_smtp_connections_rejected[5m]) > 50
        for: 10m
        labels:
          severity: warning

Grafana Dashboard

Import the dashboard from grafana/srmta-dashboard.json or create panels for:

  1. Overview — delivery success rate, queue depth, active connections
  2. Delivery Performance — latency percentiles, throughput by domain
  3. Bounce Analysis — bounce rate by type, suppressed recipients
  4. IP Health — health score per IP, disabled IPs
  5. Security — auth failures, TLS errors, rate-limited connections