An inbox for your agent, in one call.

curl -X POST https://api.mysendbox.com/v1/signup \
  -H "Content-Type: application/json" \
  -d '{ "name": "Acme booking agent", "mailbox": "bookings", "accept_terms": true }'

{
  "workspace": { "id": "tnt_01k8…", "name": "Acme booking agent", "status": "inactive" },
  "mailbox": { "id": "mbx_01k8…", "address": "bookings-k3m9qx@agentsendbox.com" },
  "api_key": "msb_live_…",
  "activate_url": "https://app.mysendbox.com/activate#act_…"
}

• name: what the workspace is called, 2 to 80 characters.
• mailbox (optional): a label for the address, 2 to 20 lowercase letters, digits or hyphens. A random suffix is added, so the address is yours alone.
• accept_terms: must be true. You accept the terms and the acceptable use policy for whoever runs you.
• Save the API key somewhere that outlasts this session (an environment variable, your secret store), and the link: they're shown once. If you lose the key, the person with the link can get you a new one.

Sending needs the plan, and the plan needs a card: that's how we keep spam off the addresses agents share. Give activate_url to the person you work for. On that page, without an account, they can:

• Start the 7-day trial for $1 (card required, not refunded), with 500 credits. Then $5 a month with 5,000 credits, unless they cancel. 1 credit sends 1 email. See pricing.
• Buy credits once the plan is live.
• Get a new API key if you lost yours (the old one stops working, unless they choose otherwise).
• Take ownership with an email sign-in, to manage billing, automatic top-up, more mailboxes and their own domains in the dashboard.

Whoever has the link can pay for and claim the workspace, so give it only to that person. Lost it? Ask for a new one (earlier links stop working).

Use the API key as a bearer token with the REST API, or with the MCP server at https://mcp.mysendbox.com/mcp.

curl https://api.mysendbox.com/v1/mailboxes/mbx_01k8…/messages \
  -H "Authorization: Bearer msb_live_…"

Every message is screened for phishing and instructions aimed at AI before you see it, and every reply is checked before it goes out. Risky replies wait for a person, the same as for any MySendbox agent.

curl https://api.mysendbox.com/v1/account \
  -H "Authorization: Bearer msb_live_…"

• workspace.status: inactive until the trial starts, then trialing, active or past_due. can_send says whether you can send now.
• credits.balance, and your mailboxes.
• POST /v1/account/activation-link: a new activation link, while nobody has claimed the workspace.

• The address replies in conversations someone else started. It doesn't start new ones: no outreach, newsletters or bulk mail (acceptable use).
• Agent addresses are on agentsendbox.com. For your own domain, and for Dispatch, a person takes ownership first.
• 3 sign-ups a day from one network.
• Not paid for or claimed within 7 days, the workspace is switched off: its key stops working and the address is removed.