Add email airdrop Motoko demo

[aterga]

What

A small self-contained Motoko demo (demos/email-airdrop/) that airdrops 1 ICP to each person who emails airdrop@<your-domain> with a valid request.

The rules (shown on the landing page, GET /)

An email is eligible when all hold:

1. The Subject contains the sender's ICP address — a 64-hex account identifier, checksum-verified (CRC32).
2. There is at least one Cc with a friend's address (a valid address that isn't the sender's).
3. The body contains, as plain substrings, both the app link and a short participation phrase (substrings, because mail clients append signatures/footers/quoted text).

Plus: one airdrop per email address, ever; rewards are paid while funds last, otherwise the sender joins a FIFO waitlist that drains automatically (a timer) or on demand (triggerWaitlist) after a top-up; and every attempt is stored (email_address → last_rewarded_at_timestamp, attempt count, last outcome).

The key design point: canisters can't receive SMTP

There is no inbound mail server on the IC, so airdrop@<domain> can't be served by the canister directly. The intended wiring is an inbound-email provider (SendGrid Inbound Parse / Mailgun Routes / Cloudflare Email Worker) that POSTs the raw message to the canister's http_request_update endpoint (guarded by a shared secret, and ideally carrying the provider's DKIM verdict). A typed submitEmail entrypoint runs the same logic for local testing. This is all laid out in the README.

Files

• main.mo — the persistent actor (eligibility, CRC32 address validation, ledger transfer, waitlist, timer, HTTP gateway + rules page).
• icp.yaml — deploys it via the @dfinity/motoko recipe.
• README.md — rules, architecture diagram, run/test instructions, threat model, and open questions.
• sample-email.txt — a ready-to-POST raw message (with a checksum-valid address).

Verification

Type-checked and compiled to Wasm against mo:base, and the trickiest pieces were exercised in the Motoko interpreter:

• a checksum-valid account id is found in the subject; a bad-checksum / missing one is rejected;
• Cc a different friend passes, Cc only yourself / empty fails;
• the raw-email parser correctly extracts From/To/Cc/Subject/DKIM/body (including Name <addr> and comma-separated Cc).

Open questions (also in the README)

This is a demo, intentionally not hardened. A few choices worth your call before going further: address format (legacy account id vs ICRC-1), one-time vs cooldown rewards, whether the Cc'd friend is a referral, requiring DKIM pass, and timer-poll vs operator-driven waitlist draining. Questions and suggestions very welcome.

🤖 Generated with Claude Code

---

Generated by Claude Code