Once Email official documentation · v1

Developer API reference

Developer API reference: Authoritative product and developer guidance for receiving temporary email, troubleshooting delivery, and testing authorized email flows safely.

Reviewed 15 August 2026

What you can do

Developer API reference: Authoritative product and developer guidance for receiving temporary email, troubleshooting delivery, and testing authorized email flows safely. POST /v1/inboxes creates an inbox and accepts Idempotency-Key; GET /v1/inboxes/{id}/messages supports since, cursor, and pageSize; detail, attachment, and DELETE /v1/inboxes/{id} complete the lifecycle. Verify the current page version and follow the linked next step; never infer a capability from a screenshot, old article, or package name.

Failures and recovery

Developer API reference: Authoritative product and developer guidance for receiving temporary email, troubleshooting delivery, and testing authorized email flows safely. Authorization uses a Bearer API Key with inboxes:create, messages:read, and inboxes:delete scopes. Responses are no-store and cross-account resources are rejected. Verify the current page version and follow the linked next step; never infer a capability from a screenshot, old article, or package name.

Security and limits

Developer API reference: Authoritative product and developer guidance for receiving temporary email, troubleshooting delivery, and testing authorized email flows safely. Stable failures are 400, 401, 403, 404, 413, 429, and 503. Respect Retry-After inside one deadline; failed creation must not consume quota and cleanup belongs in finally. Verify the current page version and follow the linked next step; never infer a capability from a screenshot, old article, or package name.