apicheats.dev Cheat sheet Raw .md
POST

Try POST /inboxes/{inbox_id}/threads/{thread_id}/emails/{email_id}/reply — Resend API

Resend playground

Reply to a thread email

Credentials

Kept in this tab only. Requests go through apicheats.dev's same-origin proxy straight to api.resend.com; the proxy stores and logs nothing about them.

Headers

Path

Body application/json

8 body fields
  • cc · optional · string — CC recipient email address. For multiple addresses, send as an array of strings. Without `reply_all`, the reply copies only these addresses. With `reply_all`, these addresses are merged with the copied recipients, without duplicates. `cc` and `bcc` combined must be fewer than 50 addresses. After the `to` recipients are added, the reply cannot exceed 50 recipients. Each address is `[email protected]` or `Name <[email protected]>`. An address that is not valid returns a 422.
  • bcc · optional · string — BCC recipient email address. For multiple addresses, send as an array of strings. BCC recipients of the original message are never copied. Each address is `[email protected]` or `Name <[email protected]>`. An address that is not valid returns a 422.
  • html · required · string — The HTML body of the reply.
  • text · optional · string — The plain-text body of the reply.
  • subject · optional · string — The subject of the reply. Cannot be only whitespace or contain a line break. When omitted, the thread subject is used, prefixed with `Re:` if it does not already start with it.
  • reply_all · optional · boolean — Reply to everyone on the original message. For a message the inbox received, the reply goes to its `Reply-To` addresses, or to its sender when it has none, and copies the other addresses of its `To` header and its `cc` recipients in `cc`. For a message the inbox sent, the reply goes to that message's `Reply-To` addresses when they are not the inbox address, otherwise to its `to` recipients, and copies its `cc` recipients. The inbox address is always excluded, and duplicates are removed.
  • attachments · optional · object[] — Files to attach, as on `POST /emails`. Each one needs `content` or `path`. The `content` of all files can total at most 25 MB. A `path` file does not count toward the 25 MB, because it is fetched when the email is sent. An empty file, a blocked file type, a `path` that does not start with `http` or that starts with `http://localhost:`, or a `content_type` that is not a valid MIME type returns a 422. Other `path` problems fail the email when it is sent, not the request.
  • headers · optional · object — Custom headers to add to the email. The `In-Reply-To`, `References` and `Reply-To` headers are set by Resend and cannot be set here. Sending one of them, in any letter case, returns a 422. Header names cannot be empty, and names and values cannot contain line breaks or null characters, or the request returns a 422. `null` means no custom headers.