Reply to an inbound email

Sends an outbound reply to the inbound email identified by id. Threading headers (In-Reply-To, References), recipient derivation (Reply-To, then From, then bare sender), and the Re: subject prefix are all derived server-side from the stored inbound row. The request body carries only the message body, optional From override, optional attachments, and optional wait flag; passing any header or recipient override is rejected by the schema (additionalProperties: false).

Forwards through the same gates as /send-mail: the response status, error envelope, and idempotent_replay flag mirror the send-mail contract verbatim.

Idempotency-Keystring

Optional client-supplied idempotency key. Retrying a request with the same key returns the original result instead of performing the action a second time; if omitted the server derives one from the canonical payload hash. Safe to retry network failures without duplicating side effects.

Request body

body_textstring

Plain-text reply body. At least one of body_text or body_html is required. The combined UTF-8 byte length of body_text and body_html must be at most 262144 bytes (same cap as send-mail).

body_htmlstring

HTML reply body. At least one of body_text or body_html is required.

fromstring

Optional override for the reply's From header. Defaults to the inbound's recipient. Use to add a display name ("Acme Support" <agent@company.com>) or to reply from a different verified outbound address (e.g. multi-team routing where support@ triages to billing@). The from-domain must be a verified outbound domain for your org, same as send-mail.

waitboolean

When true, wait for the first downstream SMTP delivery outcome before returning, mirroring the send-mail wait semantics.

Response

Outbound relay result

successtrue required

v2

Reply to an inbound email

Headers

Request body

Response