Lightweight Mail Access Monitor for Exim: Installation, Configuration, Best Practices

Mail Access Monitor for Exim Mail Server: Real-Time Tracking & Alerts

What it is
A Mail Access Monitor for Exim provides continuous visibility into who is accessing mail accounts and how — tracking IMAP/POP/SMTP authentication, mailbox reads, message deliveries, and administrative access — and raises alerts on suspicious or policy-violating activity in real time.

Key capabilities

• Authentication logging: capture successful and failed logins, including username, source IP, timestamp, auth mechanism, and client info.
• Session/activity tracking: associate authenticated sessions with mailbox actions (deliveries, fetches, deletions) when possible.
• Real-time alerts: notify on anomalies (multiple failed attempts, logins from new/geolocated IPs, simultaneous access from different regions, unusual volume).
• Correlation & enrichment: enrich events with GeoIP, ASN, hostname, and known-bad lists to prioritize incidents.
• Audit trails & reporting: searchable logs and periodic reports for compliance (e.g., HIPAA, GDPR) and internal review.
• Retention & storage options: configurable retention (locally, centralized SIEM, or log aggregation services) with secure transfer (TLS) and optional encryption at rest.
• Access controls & tamper resistance: role-based access to logs and alerts, append-only storage or WORM for compliance.

How it integrates with Exim

• Exim produces extensive logs for SMTP transactions; a monitor reads Exim mainlog and paniclog and parses authentication and delivery lines.
• For IMAP/POP sessions (fetching by mail clients or separate Dovecot/Courier), integration requires reading those services’ logs and correlating by username and timestamps.
• Optional MTA hooks: configure Exim ACLs and syslog templates to emit structured JSON log lines for easier parsing.
• Use log shipping agents (rsyslog/Fluentd/Vector/Filebeat) to forward logs to the monitor or SIEM in near real time.

Alerting rules (examples)

• 5+ failed logins for one account within 5 minutes → high-priority alert.
• Successful login from a country not previously used by the account → medium alert.
• Simultaneous logins from IPs in distant regions within 1 hour → high alert.
• Sudden spike in outbound messages from an account → high alert (possible compromise).
• Access using disabled or expired credentials → critical.

Implementation approaches

• Lightweight: log-parser + alert scripts (Python/Go) that tail Exim logs, enrich with GeoIP, and send webhook/Email/SMS alerts.
• Mid-tier: use open-source log processors (Filebeat → Elasticsearch → Kibana + Watcher or ElastAlert).
• Enterprise: forward logs to SIEM (Splunk, QRadar) with pre-built parsers and alerting rules; integrate with SOAR for automated responses.
• Hardened: implement TLS for log forwarding, sign or hash logs, store in immutable storage for compliance.

Performance & scaling

• Tail-based collectors are low-overhead; for high-volume mail servers use structured logging + batched shipping to reduce parsing cost.
• Use sampling for verbose session-level events if retention/ingest cost is a concern; keep full fidelity for auth events and alerts.

Response actions on alerts

• Automated: block offending IP via firewall or fail2ban, temporarily lock account, throttle outbound mail.
• Manual: notify admin with context (recent login history, client IPs, message counts) to investigate and remediate.

Privacy & compliance notes

• Limit retained personal data to what’s necessary for security and auditing.
• Anonymize or redact mailbox content; monitor should focus on metadata (who/when/from-where), not message bodies unless legally required.

Quick deployment checklist

1. Enable structured logging in Exim (JSON/syslog templates) where possible.
2. Configure log forwarder (rsyslog/Filebeat/Vector) to send logs securely.
3. Deploy parser/monitor (script, ELK stack, or SIEM) with GeoIP enrichment.
4. Create baseline alert rules and tune thresholds for your environment.
5. Implement incident response actions (blocklists, account lockout) and escalation paths.
6. Set retention, access controls, and periodic audit of monitor logs.

If you want, I can: provide sample Exim syslog templates, a parser script to extract auth events, example alert rules for ElastAlert, or a compact deployment playbook — tell me which.