Forward Inbox Thread Email
forward-inbox-thread-emailForward a message from a Resend inbox thread to new recipients, with optional cc, bcc, and a note. Use it to pass along a message or loop others into the conversation.
Instructions
Purpose: Forward one message from a Resend inbox thread to someone else. This sends a real email the moment you call it, from the inbox's address to the recipients named in "to", "cc" and "bcc".
NOT for: Answering the sender (use reply-to-inbox-thread-email, which answers the message's author, or everyone on it with replyAll). Not for starting a new conversation from the inbox (use send-new-inbox-email).
Returns: The sent email's id.
When to use: User asks to forward a message in an inbox thread, pass it along, or loop someone in on it. Before using this tool, you MUST double-check with the user that they want to forward this message. Reference the RECIPIENTS, including any cc and bcc, and the SUBJECT when double-checking, and warn the user that forwarding cannot be undone: a sent email cannot be recalled, and every recipient keeps the original message. You may only use this tool if the user explicitly confirms they want to forward the message after you double-check. "to" is the only body field required: html and text are an optional note of your own, because the original message is carried either way. Across to, cc and bcc a forward can reach at most 50 recipients in total. The original message's attachments are sent with the forward; name any attachments you add in the double-check. A message whose original attachment was sent from a URL cannot be forwarded. Get the emailId from get-inbox-thread.
Input Schema
| Name | Required | Description | Default |
|---|---|---|---|
| cc | No | Email address to copy on the forward, or an array of addresses. | |
| to | Yes | Recipient email address to forward to (e.g. "teammate@example.com"), or an array of recipient email addresses to forward to several. | |
| bcc | No | Email address to blind-copy on the forward, or an array of addresses. | |
| html | No | Optional HTML note to add above the forwarded message. This does not replace the original body: the message being forwarded is carried along either way. | |
| text | No | Optional plain text note to add above the forwarded message. This does not replace the original body: the message being forwarded is carried along either way. | |
| emailId | Yes | ID of the message being forwarded. This is the "id" get-inbox-thread returns for each message in the thread. | |
| headers | No | Optional custom email headers as key/value pairs (e.g. {"X-Entity-Ref-ID": "unique-id"}). Header names cannot be empty, and names and values cannot contain line breaks or null characters. In-Reply-To, References and Reply-To are reserved: Resend sets them, and passing any of them, in any letter case, fails. | |
| inboxId | Yes | Inbox ID, or the inbox email address (e.g. "support@example.com"). Not the Resend receiving address. | |
| subject | No | Subject for the forwarded email. Omit to use the thread's subject, prefixed with "Fwd:". Max 2000 characters. It cannot be only whitespace or contain a line break. | |
| threadId | Yes | Thread ID | |
| attachments | No | Files to attach. Each one needs filename plus content or url. An empty file or a blocked file type (such as .exe) is rejected. The forward also sends the attachments of the original message, and they share one limit: at most 25 MB of content together. A url file does not count toward it, because it is fetched when the email is sent. The whole email, encoded, can be at most 40 MB. | |
| idempotencyKey | No | Optional unique key that prevents duplicate sends on retries (sent as the Idempotency-Key header). Use the same key when retrying the same logical email; use a new key for a different email. Must be 1-256 characters. |