# 0lag — transactional email for agents

0lag sends transactional email through one HTTP endpoint. Once you have an API key, you can send.

## Send an email
POST https://0lag.com/v1/send
Header: Authorization: Bearer <YOUR_API_KEY>
Header: Content-Type: application/json
Body (JSON), minimal:
  {"to": "person@example.com", "subject": "Hello", "text": "Hi there"}

Optional fields: "html", "from" (must be on your assigned subdomain; defaults to
<your-handle>@<your-subdomain>), "from_name", "reply_to". Send an "Idempotency-Key" header to
make retries safe.

Every email automatically includes a one-click List-Unsubscribe header (recipients can
opt out; they then go on your suppression list). On the free tier this is mandatory. Paid
plans may set "unsubscribe": false for true transactional mail (login codes, receipts);
free-tier requests that set it return 402 upgrade_required.

Free-tier emails also append a small "Sent with 0lag" footer; paid plans send without it.

Success: HTTP 202 with {"id", "status":"accepted", "provider_message_id", ...}.

## Errors
All errors are JSON: {"error": {"code", "message", "retry_after"?}}.
- 409 domain_not_ready: your sending domain is still verifying — wait `retry_after` seconds and retry.
- 403 sender_not_allowed: the "from" address is not on your assigned subdomain.
- 429 rate_limited / quota_exceeded: slow down or you hit your plan limit.

## Orient yourself
GET https://0lag.com/v1/whoami  (with your Bearer key) → your sending subdomain, status, remaining quota.

## Full machine-readable contract
https://0lag.com/openapi.json   (OpenAPI 3.1; interactive docs at https://0lag.com/docs)