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POST
This endpoint uses a standard project API key (AS_ prefix). The reply is threaded into the original conversation (via In-Reply-To and References) and queued through the standard sending pipeline. The response returns 202 Accepted.
The from.email domain must be a verified sending domain on the project.

Authorizations

string | header
required
Project API key header of the form Bearer as_<key>. You can also pass the key via the x-api-key header.

Path Parameters

string
required
The unique identifier of the inbound message to reply to. The message must belong to the authenticated project.Example: "60d5ec49f1b2c72d9c8b1234"

Body

object
required
The sender address for the reply. The email’s domain must be a verified sending domain on the project.
string
Subject line for the reply. When omitted, defaults to the original subject prefixed with Re: (no double prefixing).Minimum length: 1Maximum length: 998Example: "Re: Question about my order"
string
HTML body of the reply.
string
Plain-text body of the reply.
object[]
CC recipients. Each entry has a required email and optional name.Maximum items: 50
object[]
BCC recipients. Each entry has a required email and optional name.Maximum items: 50
object[]
Attachments to include on the reply. Provide each attachment either inline (base64 content) or by fileUrl.Maximum items: 20

Response

Reply queued successfully (202)
boolean
Indicates if the request was successfulExample: true
string
Confirmation messageExample: "Reply queued"
object
Result of queuing the reply through the sending pipeline.

Error Responses

object
Returned when from.email is missing.
object
Returned when the from domain is not a verified sending domain on the project.
object
Returned when the inbound message does not exist or does not belong to the authenticated project, or when it has no usable reply target address.