Meta Muse

Meta Muse can use a ReplyLayer mailbox as your agent's own email address. There are two ways to connect it:

Sign in (recommended). Muse connects to ReplyLayer's MCP server at https://api.replylayer.ai/v1/mcp/oauth, and you approve it on a ReplyLayer page. No key is copied anywhere.
API key (fallback). Muse builds a custom connector from ReplyLayer's public API description, calls the REST API, and uses an agent key you enter in Muse's own credential prompt.

ReplyLayer is separate from Gmail: neither way connects a Gmail account.

For why Muse should have its own inbox, and how this compares with Meta's Gmail connector and Muse's announced address, see Give Meta Muse its own inbox, with guardrails.

Before you start

A mailbox that lets agents send. In the dashboard, open Mailboxes, choose the mailbox, and check that What agents can do is Send and draft. With Draft only or Read only, the test send fails with AGENT_SENDING_DISABLED. Saving the change asks you to confirm your sign-in.
A mailbox that can start a new email. After you upgrade from the trial, the trial mailbox keeps receiving and can reply in existing threads, but a new email from it fails with ESTATE_CONTINUITY_REPLY_ONLY. Use your sending mailbox, or set one up, at app.replylayer.ai/mailboxes. See Tiers, quotas, and sandbox limits.
For the API-key way only: an agent key for that mailbox, created on app.replylayer.ai. The full key is shown once. See Creating a key. Signing in needs no key.

Connect Muse by signing in

In the dashboard, open Connect Agent, choose the mailbox, and choose Meta Muse in Step 3. You don't need the agent key from Step 2.
Copy the test prompt. It gives Muse the connection URL, https://api.replylayer.ai/v1/mcp/oauth, and the exact sign-in addresses (authorization server metadata, authorize and token endpoints), and names your mailbox and a test token. It never contains a key or the client ID. Without the sign-in addresses Muse may guess wrong ones and stop.
Start a new chat in Muse and paste the prompt.
When Muse's connect window asks for a client ID, enter meta-muse.
A ReplyLayer page opens: Connect Meta Muse (agent.meta.ai) to ReplyLayer. Sign in if it asks.
Choose the mailboxes Muse may use, including the one you chose on Connect Agent, then choose Approve. ReplyLayer may ask you to confirm your sign-in first. Muse can use only the mailboxes you choose, with the same limits as an agent key.

Muse lists your mailboxes, sends one email to the simulator, and reports the result. ReplyLayer emails you when you approve a new connection.

Connect Muse with an API key

Use this if signing in doesn't work for you.

In the dashboard, open Connect Agent, choose the mailbox, and choose Meta Muse in Step 3.
Create the agent key in Step 2 if you do not have one.
Open Connect with an API key instead and copy the API-key test prompt. It names your mailbox and a test token. It never contains your key.
Start a new chat in Muse and paste the prompt.
When Muse shows its ReplyLayer connector card, choose Connect and paste the key into the credential prompt that opens. This is the only place the key goes. Never paste it into the chat.
When Muse asks to share info with api.replylayer.ai, allow it.

Muse lists your mailboxes, sends one email to the simulator, and reports the result.

Reading the result

Muse reports email_effect.effect_status and the message id. Send outcomes defines every value.

sent: ReplyLayer accepted the test email. It does not confirm delivery.
held_for_review: the email is waiting for a person on your account to approve or deny it in the dashboard. Muse cannot approve it.
held_infrastructure: a temporary problem held the email before it was checked. Wait, then choose Start a new test on Connect Agent and paste the new prompt. The same prompt returns the same hold.
blocked: ReplyLayer refused the email. Do not ask Muse to rewrite it. See Content scanning.

Pasting the same prompt again never sends a second email. ReplyLayer returns the first result for the same idempotency key.

If Muse reports an error

Muse reports	What to do
`401`	With sign-in: the connection was revoked or has ended. Connect again the same way. With an API key: ReplyLayer refused the key. Check that it is an active agent key created on app.replylayer.ai for this mailbox. If you no longer have it, create a new one and give it to Muse through its credential prompt.
`429`	Too many requests. Wait before trying again, and do not ask Muse to retry in a loop. If it follows a `401`, fix the key first.
`AGENT_SENDING_DISABLED`	Set What agents can do to Send and draft on the mailbox page, then paste the same prompt again.
`ESTATE_CONTINUITY_REPLY_ONLY`	Choose your sending mailbox (set up at app.replylayer.ai/mailboxes) on Connect Agent and paste the new prompt. With sign-in, first add that mailbox to Muse's connection under API keys → Connected apps; with an API key, create a key for it.
`RECIPIENT_AGENT_CONTAINED`	Stop. Why a send was refused explains who can lift it.
`SANDBOX_RECIPIENT_NOT_VERIFIED`	On the free Sandbox the person is not one your account can email yet. See Emailing real people.
`RECIPIENT_WRITE_AGENT_CONTAINED`	The mailbox limits Muse to people you approve, or is not set to Send and draft, so Muse cannot add people itself. Add the person on the Recipients page, then ask Muse to try again.
`INSUFFICIENT_SCOPE` when Muse tries to add a recipient	Adding recipients from an agent isn't available right now. Add the person on the Recipients page, and once they are confirmed or added, ask Muse to try again.
An answer with no new request	Muse may answer from an earlier result. Ask it to make the call again with the same idempotency key.

Emailing real people

On the free Sandbox you can email your own address and anyone who confirms by link, reply to people who write to you from an authenticated address, and add up to 5 people you know, yourself or through your agent. Add $5 of pay-as-you-go credit or upgrade to email anyone.

Your agent can add people itself, or ask them to confirm by link, unless you restrict it to people you approve or to drafting only; then it asks you. If someone added without a click reports your email as spam, everyone added that way must confirm by link before you can email them again and your trial can no longer add people that way; a report from a second person suspends the Sandbox account.

So when Muse needs to email someone new, it can add them as someone you know when you tell it you know them, and then send; otherwise it asks them to confirm by link, and it can send once they click. If the mailbox is restricted to people you approve (Only let this agent email people I approve on Connect Agent) or is not set to Send and draft, Muse cannot add anyone: add the person on the Recipients page, then ask Muse to try again. See Tiers, quotas, and sandbox limits.

After the test

Muse keeps the connection. It can use ReplyLayer's other tools (or, with an API key, other operations in the API description), limited to what an agent key for this mailbox may do. See Roles: admin vs agent.

Signed in. The connection is listed as Meta Muse under API keys → Connected apps. Revoke it there to disconnect Muse; its next call fails. A connection also ends after 30 days without use, and at the latest 90 days after you approve it; then connect again the same way.

API key. Muse has no settings page for a connector's key. To replace the key, create a new agent key, then ask Muse in a chat to replace the API key for its ReplyLayer connector. Muse shows the connector card again: choose Connect and enter the new key in the window that opens, never in the chat. Check that Muse can list your mailboxes, then revoke the old key. See Rotating keys. A revoked key stops working in Muse at once.