FreeBSD 13 Sendmail Queue Builds Up and Mail Stalls

📖 ~1 min read

Table of contents

1. Symptom & Impact
2. Environment & Reproduction
3. Root Cause Analysis
4. Quick Triage
5. Step-by-Step Diagnosis
6. Solution – Primary Fix
7. Solution – Alternative Approaches
8. Verification & Acceptance Criteria
9. Rollback Plan
10. Prevention & Hardening
11. Related Errors & Cross-Refs
12. References & Further Reading

Symptom & Impact

Local or relay mail delivery can stall on FreeBSD 13, causing backlog in the sendmail queue.

Environment & Reproduction

mailq grows, periodic reports do not deliver, and logs show deferred connection or DNS errors.

Root Cause Analysis

Relay host connectivity failures, DNS resolution issues, or restrictive firewall policy frequently block delivery.

Quick Triage

Run mailq, check service sendmail status, and inspect /var/log/maillog for repeated deferral reasons.

Step-by-Step Diagnosis

Assess queue growth rate and critical message impact. image_ref=0

Solution – Primary Fix

Correct relay or resolver settings, reload sendmail config, and process queue with sendmail -qv. image_ref=1

Solution – Alternative Approaches

Use service sendmail restart after configuration changes and ensure startup flags are set in rc.conf.

Verification & Acceptance Criteria

Keep host and relay parameters consistent and avoid conflicting smart host directives.

Rollback Plan

Allow SMTP egress in pf and verify destination MX hosts are reachable over expected routes.

Prevention & Hardening

Send test messages, watch maillog, and confirm queue depth declines to normal levels.

Related Errors & Cross-Refs

Monitor queue size metrics and alert when deferred counts exceed operational thresholds.

Related tutorial: View the step-by-step tutorial for freebsd-13.

View all freebsd-13 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Consult man sendmail, FreeBSD mail configuration docs, and resolver troubleshooting resources.