OTPBox

Disposable e-mail for AI agents

E-mail inboxes your AI agent can read.

OTPBox gives your agent its own throwaway addresses. It signs up on any site, then reads the one-time code or the verification link through MCP or the REST API. No shared mailbox, no IMAP, no copying codes by hand.

Get started See how it works

Included in rc.center Pro, US$ 9/month.

  • Receive-only
  • Encrypted per account
  • MCP and REST

How it works

From sign-up form to code in three steps

The same flow works for an agent in a chat, a test runner or a CI job.

  1. Create an inbox

    Your agent calls inbox_create (or POST /v1/inboxes) and gets a fresh address on your own subdomain.

  2. Use it to sign up

    It types the address into the sign-up form, the magic-link login or the password reset. Our receive-only servers take the mail and seal it with your account's key.

  3. Read the code

    message_wait waits until the mail lands and returns the one-time codes, best match first, and the verification link. Prefer push? Set a signed webhook per inbox.

Addresses look like signup.k3m9qa@<account>.otpbox.org (or .otpbox.top). The account part is a random subdomain that belongs to you alone.

Use cases

For software that has to read its own mail

AI agents that sign up and log in

Give Claude or your own agent an address it controls, so it can finish sign-ups, magic-link logins and e-mail codes without asking you to paste anything.

End-to-end tests of sign-up flows

Each Playwright or Cypress run creates its own inbox, submits the form and checks the real e-mail, code and link included.

CI pipelines

One HTTP call creates the inbox, another waits for the message with a timeout. API keys work headless: no browser, no IMAP.

Transactional e-mail checks

Confirm that your own password reset, invite and receipt e-mails arrive, with the right subject and links, plus their SPF, DKIM and DMARC results.

Works with

Any MCP client, or plain HTTP

Connect once with your rc.center account. MCP clients sign in with OAuth and you approve each permission.

Claude on claude.ai

Settings, Connectors, Add custom connector. Paste this URL and connect:

https://otpbox.rc.center/mcp

Claude Code

Run this, then /mcp inside Claude Code to sign in:

claude mcp add --transport http otpbox https://otpbox.rc.center/mcp

Cursor

Add this to ~/.cursor/mcp.json:

{"mcpServers": {"otpbox": {"url": "https://otpbox.rc.center/mcp"}}}

Codex

Add the server and sign in:

codex mcp add otpbox --url https://otpbox.rc.center/mcp
codex mcp login otpbox

REST API

Create an API key in the web app and send it as a bearer token. The same features, described in /v1/openapi.json:

curl -s -X POST https://otpbox.rc.center/v1/inboxes \
  -H "Authorization: Bearer $OTPBOX_KEY" \
  -H 'Content-Type: application/json' -d '{"prefix":"signup"}'

curl -s "https://otpbox.rc.center/v1/inboxes/$INBOX_ID/wait?timeout=60&subject=verification" \
  -H "Authorization: Bearer $OTPBOX_KEY"

Any MCP client

Streamable HTTP with OAuth 2.1: dynamic client registration and PKCE. You see every connected app and can disconnect it at any time.

12 MCP tools, each with a REST twin:

  • inbox_create
  • inbox_list
  • inbox_get
  • inbox_delete
  • inbox_webhook_set
  • inbox_webhook_clear
  • messages_list
  • message_get
  • message_wait
  • message_delete
  • attachment_get
  • usage_get

Read the full docs

Security and privacy

Mail is private and hostile. We treat it that way.

Pricing

Part of rc.center Pro

One rc.center subscription covers OTPBox and the AI hub.

Promotional price for a limited time; subscribers are notified before any change. The free rc.center plan does not include OTPBox.

rc.center Pro

Promotional price

US$ 9/month

or R$ 49/month in Brazil

  • 20 active inboxes
  • 1,000 messages per month
  • Up to 30 messages per minute
  • 30-day retention
  • Messages up to 10 MB
  • 1 GB of encrypted storage
  • MCP, REST API and signed webhooks

Also included: the AI hub with unlimited vault items.

Subscribe at rc.center Already on Pro? Sign in

FAQ

Questions, answered

Is OTPBox free?

No. OTPBox is part of the rc.center Pro plan: US$ 9/month, or R$ 49/month in Brazil. A free rc.center account can sign in, but creating inboxes needs Pro.

Which domains and addresses do I get?

Addresses end in <account>.otpbox.org or <account>.otpbox.top, where <account> is a random subdomain that only your account receives on. The inbox part is an optional prefix you choose plus a random part. A +tag after the local part still reaches the same inbox.

How long are messages kept?

Until your plan's retention ends: 30 days on Pro. Then they are deleted from the index and from storage. You can delete a message or a whole inbox earlier at any time.

Can OTPBox send e-mail?

No. OTPBox is receive-only. It never sends mail from its domains, so it cannot be used for outreach or replies.

Can I use it for mass sign-ups?

No. Mass sign-ups on third-party services and any illegal use are forbidden. Each account has inbox, per-minute and monthly limits, and accounts that abuse the service are suspended.

How do I connect Claude?

On claude.ai, add a custom connector with the URL https://otpbox.rc.center/mcp. In Claude Code, run: claude mcp add --transport http otpbox https://otpbox.rc.center/mcp, then /mcp to sign in with rc.center.

Do I need MCP?

No. Everything the MCP tools do is also in the REST API, with API keys for scripts and CI, and per-inbox webhooks if you prefer push.

Give your agent an inbox.

Sign in with rc.center, connect your MCP client and create your first address.

Get started