The Difficult Email Writer

Help me write this difficult or high-stakes email well.

The situation: [DESCRIBE — PUSHBACK, BAD NEWS, SENSITIVE ASK, CONFLICT]
The recipient and relationship: [DESCRIBE]
What I need to achieve: [DESCRIBE]

Provide:
1. Whether email is even the right medium (or if this needs a conversation)
2. A version that's clear, professional, and gets the outcome
3. The tone calibrated to the relationship and stakes
4. What to say and firmly avoid (nothing I wouldn't want forwarded)
5. A crisp subject line and a clear ask/next step

Help me be direct without being cold, and firm without burning the bridge.