MTA-STS self-hosting
Hosts https://mta-sts.<domain>/.well-known/mta-sts.txt directly from this
Worker, served publicly (no Access/token gate — real mail senders must reach it unauthenticated). Saving here
only writes to this project's own database; it does not touch DNS or Cloudflare routing —
you still need to add the Worker route and DNS records shown after saving, one time per domain. Opt-in per
domain, separate from the Domains allowlist. See the Setup guide
for the full walkthrough — the Worker route and DNS record steps are easy to get wrong.