DNS Resolver Architecture
Design local recursive resolution, caching, observability and failure handling.
Production review required. Validate every directive against your licensed PowerMTA release, traffic model, provider policies and security controls.
Operational objective
Design local recursive resolution, caching, observability and failure handling.
The design goal is predictable behavior, clear ownership, measurable outcomes and safe rollback.
Architecture principles
- Separate traffic where failure domains differ
- Keep source identity stable and documented
- Preserve attribution from submission through delivery
- Monitor queue age, outcomes and complaints by stream
- Design recovery before increasing capacity
Illustrative baseline
# Illustrative architecture fragment for DNS Resolver Architecture
# Replace all example values and verify directive names.
<virtual-mta enterprise-stream>
smtp-source-host 192.0.2.25 mail.example.com
</virtual-mta>
<domain *>
max-smtp-out 2
retry-after 20m
bounce-after 4d
</domain>This fragment is intentionally conservative and incomplete. It demonstrates structure, not a universal production policy.
Implementation workflow
- Document requirements and failure boundaries.
- Create a minimal staged configuration.
- Validate syntax and routing with controlled test identities.
- Observe accounting, queue and provider outcomes.
- Roll out gradually with an explicit rollback trigger.
Metrics and evidence
| Metric | Why it matters | Action threshold |
|---|---|---|
| Queue age | Shows delivery lag | Investigate sustained growth by provider and VMTA |
| Temporary failure rate | Shows throttling or policy pressure | Group by SMTP response family before tuning |
| Hard bounce rate | Shows recipient quality | Suppress invalid recipients immediately |
| Complaint rate | Shows expectation or permission problems | Pause and investigate affected stream |
Common failure modes
- Changing several controls simultaneously.
- Using shared credentials or sender identities.
- Increasing throughput before understanding queue growth.
- Applying generic provider settings to every stream.
- Operating without tested backup and rollback procedures.
Production checklist
- Configuration validated in staging
- DNS and authentication verified
- Monitoring and alerts confirmed
- Rollback package prepared
- Change owner and review window assigned