The short answer
Meta Muse can help plan a letter and, where its browser access works, assist with the IRIS website. The practical consumer route is to prepare a final US Letter PDF, open /letters/send, upload the file yourself if needed, and personally review the document, addresses, options, and total before paying. Meta has not documented an arbitrary MCP connector for the consumer Muse app; Muse Code is a separate developer tool that supports remote MCP servers.
Muse the personal agent is not Muse Code
Meta describes the consumer Muse app as a personal agent available in the US on mobile and muse.ai. It can open a browser and fill forms, and it asks for approval before sensitive actions such as purchases. Those general capabilities do not establish an IRIS integration, reliable local-file handoff, or an IRIS checkout flow that Muse can complete.
Muse Code is Meta's separate coding agent. Its documentation describes MCP server configuration, including remote streamable_http transport. Use the consumer website route for an occasional letter; consider Muse Code only if you control a trusted local development workflow.
Give Muse a bounded preparation task
Ask Muse to draft from approved facts or make a checklist of missing details, not to invent dates, addresses, legal claims, prices, or a signature. Check the text against your records, then export and inspect a finished US Letter PDF. If the letter contains private customer or financial information, share only what Muse needs for the drafting task; you can skip the assistant entirely for sensitive content and use IRIS directly.
A useful instruction is: “Help me prepare a one-page customer letter from these approved facts. Mark unknown details for my review. Do not send mail, enter payment details, or claim an order was placed.” Review the final PDF, not just Muse's chat response: page breaks and address placement can change during export.
Use the IRIS website, with a manual fallback
Open IRIS /letters/send for a finished US Letter PDF. If you allow Muse to navigate the site, ask it to explain the steps and help with non-sensitive form entry while you watch. IRIS asks for the PDF, return address, recipient address, printing and mailing options, then review and payment. Confirm each value against your records rather than trusting a browser agent's interpretation.
Do not assume Muse can access a PDF on your device or upload it into its browser. If file selection, sign-in, or another step is unavailable or uncertain, take control and do that step yourself. You do not need an API key or a Muse connector for the consumer website path.
Keep the paid mailing decision with a person
Before checkout, open the uploaded PDF and check every page, the sender and recipient addresses, print options, total price, and your authority to send. Correct any mistake and review the revised file and details again. Handle checkout and payment yourself; do not treat Meta's general purchase-approval description as proof that Muse supports or completes IRIS payment.
Keep the resulting confirmation or order reference and check status later. A draft, a filled form, and a quoted price are not mailed letters. Meta says people can control connected-app access and view an audit trail, but you should still avoid granting unrelated account access just to prepare one mailing.
Optional: use Muse Code and IRIS MCP for a repeatable workflow
In Muse Code's settings, a developer can configure the IRIS remote streamable_http MCP endpoint at https://api.irispostalforms.com/mcp with a bearer API key kept in trusted local configuration or environment storage, never in prompts or a public repository. IRIS requires account:read for MCP requests. A preparation key needs account:read, documents:write, and mailings:read; only a separately authorized submission step additionally needs mailings:write.
For an existing local PDF, call create-document-upload to obtain the private uploadUrl and uploadHeaders. MCP does not transfer the PDF bytes: trusted local code must PUT the exact file bytes to that URL using every returned upload header, verify the PUT succeeded, then register-document and quote-mailing. Stop and show a human the exact PDF, addresses, options, and quoted price. Only after explicit approval should authorized code call create-mailing with a saved idempotency key, record the returned orderId, and use get-mailing-status to check progress. This developer path is not a capability of the consumer Muse app.
Sources & further reading
Product details checked against the IRIS API contract when this article was published. Platform references can change; consult the linked documentation when implementing.
- Meta: Introducing Muse, the personal AI agent
- Meta: Extending Muse Code with MCP
- IRIS API documentation
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