Response format & errors

PostTo decides how to respond based on one thing: whether your request looks like a plain browser form submission, or an API call.

Two response modes

If your request has no Accept: application/json header — the default for a plain HTML <form> — a successful submission gets a redirect to a hosted success page, and a failed one gets a rendered error page. This is the zero-JavaScript path: your form works with no code beyond the HTML tag itself.

Send Accept: application/json and you get JSON back instead, for both success and failure. Use this from a fetch call if you want to show your own success/error state without a full page reload. Signed-mode (server-to-server) requests always get JSON, since there's no browser to redirect.

Success response

HTTP 200, with the new submission's ID and its initial status:

{ "id": "sub_01JXF...", "status": "pending" }

status is pending immediately after a successful POST. It updates in the dashboard (and in the webhook payload, if you have one configured) once spam filtering and delivery finish — usually within a second or two.

Submission statuses

Status	Meaning
`pending`	Received, being processed
`delivered`	Sent to your destination email
`flagged`	Delivered, but scored as possible spam — worth a glance in the dashboard
`held`	Blocked by spam filtering, not delivered automatically — reviewable and releasable from the dashboard
`unscored`	Delivered; AI spam classification was skipped or unavailable, so only the baseline check ran
`failed`	Delivery to your inbox failed after retries — retry manually from the dashboard

Error response

A non-2xx status, with a machine-readable code and a human-readable message:

{ "error": "rate_limited", "message": "Too many requests. Please wait a moment and try again." }

Build your integration to branch on error, never on message. error is a stable code that won't change wording or language; message is just for humans and may be reworded at any time.

Error codes

Code	HTTP status	Meaning
`not_found`	404	The token in the URL doesn't match any endpoint
`endpoint_paused`	403	The endpoint has been paused by its owner
`endpoint_unverified`	403	The destination email hasn't been verified yet
`origin_not_allowed`	403	The request's Origin header isn't in the endpoint's domain allowlist
`invalid_signature`	401	Signed mode: the HMAC signature is missing, wrong, or expired
`turnstile_failed`	403	Cloudflare Turnstile human verification failed
`quota_exceeded`	402	The account's monthly submission quota has been reached
`empty_submission`	422	The request body had no fields in it
`rate_limited`	429	Too many submissions in a short window — see Rate limits

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