How to Connect Claude to Cold Email

Short answer: Claude connects to outside tools through custom connectors, which Anthropic launched on 1 May 2025 (then called Integrations) and opened to Pro on 3 June 2025. A custom connector is a remote MCP server on the public internet. The hosted Outreach2day MCP server is live at https://public.outreach2day.com/mcp and signs in with OAuth (since 29 September 2026), so in Claude Desktop and claude.ai you add the URL as a custom connector and sign in with your Outreach2day account; no API key needed. Claude Code adds it with claude mcp add and signs in from /mcp. Claude then checks domains, quotes mailboxes, runs warm-up and reads replies; you approve each order and pay on Stripe.

Checked September 2026 against Get started with custom connectors, Authentication for connectors Anthropic's Integrations announcement and Connect to local MCP servers.

Connection Methods

Custom connectors are available on Free, Pro, Max, Team and Enterprise plans; Free accounts are limited to one. On Team and Enterprise only an Owner can add a connector for the organization. The server must be reachable from Anthropic's IP ranges, because the connection runs from Anthropic's cloud even when you use the desktop app.

What Claude Can Do With Your Cold Email Setup

The hosted server gives Claude tools for domains, quotes, mailboxes, warm-up, campaigns and replies. If you run the read-only local server from our cold email MCP server guide instead, Claude Desktop has six tools:

That covers the questions people ask most: "is my setup ready to send", "which mailboxes are still warming", "what came back this week". Starting warm-up and adding mailboxes to a sequencer are covered in the follow-up posts on warm-up tools and domains and mailboxes. Buying domains stays out of these tools on purpose.

Connect Claude Desktop to Outreach2day, step by step

1. Open Connectors. In Claude Desktop or claude.ai, open Customize, Connectors, click + and choose Add custom connector

2. Paste the server URL. Enter https://public.outreach2day.com/mcp and click Connect; no API key is asked for

3. Sign in. Claude opens the Outreach2day sign-in page; sign in and allow access. The connector then works in claude.ai, Claude Desktop and the mobile apps

4. Test with a read-only question. Ask "Which of my mailboxes are still warming?"; Claude asks before each tool call; approve it and compare the answer with the app

Remote servers go in as connectors, not in claude_desktop_config.json. That file is only for a local server you run yourself: to use the read-only server from our cold email MCP server guide, create a key only for Claude on the API keys page and save it to a file readable only by you: ~/.outreach2day.env with export OUTREACH2DAY_API_KEY=..., chmod 600. Open the config in Claude Desktop under Settings, Developer, Edit Config (~/Library/Application Support/Claude/claude_desktop_config.json on macOS), and add the entry below with absolute paths and your workspace ID. The key is read from the file when the server starts, so it stays out of the config (macOS and Linux):

{
  "mcpServers": {
    "outreach2day-local": {
      "command": "/bin/sh",
      "args": ["-c", ". \"$HOME/.outreach2day.env\" && exec /path/to/.venv/bin/python /path/to/o2d_mcp.py"],
      "env": {
        "O2D_WORKSPACE_ID": "123"
      }
    }
  }
}

Use a key you can revoke on its own.

Add the Server in Claude

In Claude Desktop or claude.ai (the connector then also works in the browser and on mobile): Customize, Connectors, click + and choose Add custom connector, paste https://public.outreach2day.com/mcp, click Connect and sign in with your Outreach2day account. Free plans can add one custom connector. The manual config and each client's steps are on the MCP page for Claude.

Or open the Add to Claude link, which fills in the dialog.

For Claude Code on your computer, one command adds the server; then sign in from /mcp:

curl -fsSL https://outreach2day.com/install | sh -s -- --client claude

On Windows, in PowerShell: $env:O2D_CLIENT="claude"; irm https://outreach2day.com/install.ps1 | iex. The installer asks for no API key. It adds the server to Claude Code by URL (sign in from /mcp afterwards) and prints the connector steps for Claude Desktop, which takes remote servers as custom connectors rather than through claude_desktop_config.json.

Prompts to Try in Claude

• "Which mailboxes have warmed for at least 14 days and are ready for cold email? Group them by domain."

• "Check whether acmemail.com, tryacme.com and getacme.info are free. Do not buy anything."

• "Summarise this week's replies marked interested, one line each, with the sender."

• "I want to send 1,500 cold emails a day. At 25 per mailbox and 5 mailboxes per domain, how many do I have and how many more do I need?"

Fifteen more, grouped by task, are in Claude prompts for cold email.

Limits and Safety

• Approve tool calls. Claude asks before calling a tool. "Allow always" is fine for the read-only tools above; keep anything that writes on manual approval.

• API limits and key safety: cold email API.

FAQ

Can I add Outreach2day to claude.ai as a custom connector today?

Yes. Claude.ai custom connectors sign in with OAuth, which the Outreach2day MCP server has supported since 29 September 2026: add https://public.outreach2day.com/mcp under Customize, Connectors and sign in. No API key is needed; Claude Code signs in the same way from /mcp.

Which Claude plans support custom connectors?

Free, Pro, Max, Team and Enterprise, per Anthropic's help center. Free accounts can add one custom connector. On Team and Enterprise an Owner adds it for the organization.

Can a custom connector use an API key instead of OAuth?

Anthropic documents a static credential (an API key or bearer token entered once by an organization Owner) as a beta available to a limited set of organizations. OAuth is the general option.

Does the local server work in claude.ai in the browser?

No. Servers in claude_desktop_config.json run only in Claude Desktop. They are not available in claude.ai or Cowork.

Can Claude send cold emails through Outreach2day?

Yes, through a campaign on the hosted Outreach2day MCP server: Claude builds the sequence and launch_campaign runs after 14 days of warm-up, a passed preflight and your yes in the chat. The local read-only server has no send tool.

Related

• Outreach2day MCP for Claude: what the hosted MCP server covers

Create an account, add the connector and sign in from Claude; for a local server or CI, create a key on the API keys page.