curl -X PATCH 'https://api.resend.com/inboxes/inbox-id/drafts/draft-id' \
  -H "Authorization: Bearer $RESEND_API_KEY" \
  -H 'User-Agent: my-app/1.0' \
  -H 'Content-Type: application/json' \
  -d '{
  "to": [
    "ada@example.org"
  ],
  "cc": "example-cc",
  "bcc": "example-bcc",
  "subject": "Refund issued for order 1041",
  "html": "<p>It works!</p>",
  "text": "example-text",
  "attachments": [
    {
      "content": "aGVsbG8gZTJl",
      "filename": "receipt.pdf",
      "content_type": "application/pdf"
    }
  ]
}'

# PATCH /inboxes/{inbox_id}/drafts/{draft_id} (Resend API)
Base URL: https://api.resend.com
Auth: Authorization: Bearer <RESEND_API_KEY>
Last verified: 2026-10-20

> Update an existing draft

## Critical Gotchas
* All requests must include a `User-Agent` header (e.g. `User-Agent: my-app/1.0`) or the API returns HTTP 403.
* The `to` field accepts either a single recipient email address string or an array of strings for multiple recipients (max 50).

## cURL
curl -X PATCH 'https://api.resend.com/inboxes/inbox-id/drafts/draft-id' \
  -H "Authorization: Bearer $RESEND_API_KEY" \
  -H 'User-Agent: my-app/1.0' \
  -H 'Content-Type: application/json' \
  -d '{"to":["ada@example.org"],"cc":"example-cc"}'

## Parameters
| Name | In | Type | Required | Description |
| :--- | :--- | :--- | :--- | :--- |
| inbox_id | path | string | Yes | The Inbox ID or the inbox email addre... |
| draft_id | path | string | Yes | The Draft ID. |
| to | body | string | Yes | The recipients. For multiple addresse... |
Other params: cc, bcc, subject, html, text, attachments

## Response (200 OK)
{"object":"inbox_draft","id":"c3a1e8b4-2d5f-4a7c-9e10-6b8d7f5a4c32"}

---
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PATCH

PATCH /inboxes/{inbox_id}/drafts/{draft_id} — Resend API

Resend API

Update an existing draft

Base URL: https://api.resend.com
Auth: Authorization: Bearer <RESEND_API_KEY>
Last verified: 2026-10-20 · upstream hash matched

Actions Try in browser→

Agents: curl -H "Accept: text/markdown" this URL
→ 229 tokens · Vary: Accept

Critical gotchas

All requests must include a User-Agent header (e.g. User-Agent: my-app/1.0) or the API returns HTTP 403.

The to field accepts either a single recipient email address string or an array of strings for multiple recipients (max 50).

cURL

curl -X PATCH 'https://api.resend.com/inboxes/inbox-id/drafts/draft-id' \  -H "Authorization: Bearer $RESEND_API_KEY" \  -H 'User-Agent: my-app/1.0' \  -H 'Content-Type: application/json' \  -d '{  "to": [    "[email protected]"  ],  "cc": "example-cc",  "bcc": "example-bcc",  "subject": "Refund issued for order 1041",  "html": "<p>It works!</p>",  "text": "example-text",  "attachments": [    {      "content": "aGVsbG8gZTJl",      "filename": "receipt.pdf",      "content_type": "application/pdf"    }  ]}'

Parameters

Name	In	Type	Required	Description
inbox_id	path	string	Yes	The Inbox ID or the inbox email address, such as `[email protected]`. A value that contains `@` must be a valid email address, and any other value must be a UUID, or the request returns a 422. The address match is case-insensitive and never falls back to the inbox `name`. An address that matches no inbox returns a 404.
draft_id	path	string	Yes	The Draft ID.
to	body	string	Yes	The recipients. For multiple addresses, send an array of strings. Each value can include a friendly name. Pass `null` to clear. Each address is `[email protected]` or `Name <[email protected]>`. An address that is not valid returns a 422.
cc	body	string	No	The CC recipients. Pass `null` or `[]` to clear. Each address is `[email protected]` or `Name <[email protected]>`. An address that is not valid returns a 422.
bcc	body	string	No	The BCC recipients. Pass `null` or `[]` to clear. Each address is `[email protected]` or `Name <[email protected]>`. An address that is not valid returns a 422.
subject	body	string	No	The subject. Max 2000 characters. Cannot be only whitespace or contain a line break. Pass `null` to clear.
html	body	string	No	The HTML body. Pass `null` to clear.
text	body	string	No	The plain text body. Pass `null` to clear.
attachments	body	object[]	No	Files to store on the draft. Each one needs `content`, `filename` and `content_type`. A `path` without `content` returns a 422, and when both are sent, `path` is ignored. A `content_id` returns a 422. The files on a draft can total at most 25 MB. An empty file or a blocked file type returns a 422. Sending the field replaces every attachment on the draft. Send `[]` to remove them all. `null` also removes them all.

Response 200 OK

{
  "object": "inbox_draft",
  "id": "c3a1e8b4-2d5f-4a7c-9e10-6b8d7f5a4c32"
}

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