2026-02-16

The POST /v1/emails and PATCH /v1/emails/{id} endpoints now reject bodies that start with YAML frontmatter (a --- delimiter followed by key-value pairs). This is almost always a sign of a bug in your integration rather than intentional email content, so the API now returns a 400 with the code body_contains_frontmatter.

If you need to bypass this restriction, pass the X-Buttondown-Live-Dangerously header:

curl -X POST "https://api.buttondown.com/v1/emails" \
  -H "Authorization: Token YOUR_API_KEY" \
  -H "X-Buttondown-Live-Dangerously: true" \
  -H "Content-Type: application/json" \
  -d '{"subject": "My email", "body": "---\nstatus: sent\n---\nBody"}'