- HMTP redesigns email on top of HTTP, replacing SMTP components with existing technologies like WebFinger, ActivityPub, and HPKE.
- Discovery and delegation use a static JSON document at `.well-known/hmtp/user`, enabling per-user inbox delegation without DNS changes.
- Identity is anchored to a domain with sigchains for key rotation, with domain control as a fallback for lost keys.
- Delivery uses store-and-forward via POST to the recipient's inbox, with idempotent retries based on content hash for deduplication.
- Messages are signed and optionally encrypted; sender verification is done by fetching the sender's public key from their `.well-known` document.
- Anti-spam layers include identity cost (domain ownership), first-contact consent (requests box), and optional postage (HTTP 402).
- Reading and synchronization use JMAP over HTTP, with push notifications via SSE or WebPush.
- A working prototype in Python is available, covering signed delivery, encryption, deduplication, and key rotation.