Post-mortem template exists

Without a post-mortem template, email incidents end when sends resume — the root cause, contributing factors, and action items are never formally captured. The same misconfiguration repeats. NIST SP 800-53 IR-5 (Incident Monitoring) and ISO 25010 reliability.recoverability both require that incidents are tracked and that learnings feed back into system improvements. A template is not bureaucracy — it is the mechanism that converts a painful incident into a concrete backlog item that prevents recurrence.

Create docs/templates/post-mortem.md with at least five sections:

# Incident Post-Mortem

**Date:** YYYY-MM-DD
**Severity:** P1 / P2 / P3
**Duration:** HH:MM (detection to resolution)
**Affected:** [N emails affected] [N contacts impacted]

## Timeline
- HH:MM — [event]

## Root Cause
[One paragraph]

## Contributing Factors
- [Factor]

## What Worked
- [Item]

## What Didn't Work
- [Item]

## Action Items
| Action | Owner | Due |
|--------|-------|-----|
| | | |

Reference this template from the deliverability incident runbook (docs/runbooks/deliverability-incident.md) so it is findable after every incident. A template with fewer than 5 sections does not satisfy this check.