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 in early access, so today you connect Claude through Claude Desktop with a small local MCP server over the Outreach2day REST API. It reads domains, mailboxes, warm-up state and replies. On claude.ai in the browser, without a remote server, Claude works from data you paste or upload.

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

With the local server from our cold email MCP server guide, Claude Desktop has six read-only 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. Buying domains through the API is paid right away — give an agent a billing-scoped key only if you want it to buy.

Connect Claude Desktop to Outreach2day, step by step

1. Create an API key. In the app, open the API keys page and create a key only for Claude (ot2d_...). It acts as your user in every workspace you belong to; the server pins it to one workspace ID.

2. Save the server script. Copy o2d_mcp.py from the cold email MCP server guide and install its two dependencies in a virtual environment (mcp and requests).

3. Open the config file. In Claude Desktop, go to Settings, then Developer, then Edit Config. On macOS the file is ~/Library/Application Support/Claude/claude_desktop_config.json; on Windows %APPDATA%\Claude\claude_desktop_config.json.

4. Add the server entry. Paste the block below with absolute paths, your key and your workspace ID, then restart Claude Desktop.

5. 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.

{
  "mcpServers": {
    "outreach2day": {
      "command": "/path/to/.venv/bin/python",
      "args": ["/path/to/o2d_mcp.py"],
      "env": {
        "O2D_API_KEY": "ot2d_...",
        "O2D_WORKSPACE_ID": "123"
      }
    }
  }
}

The config file is plain text. Keep it out of shared or synced folders, and use a key you can revoke on its own.

The Custom Connector (Early Access)

A custom connector would let you use Outreach2day from claude.ai in the browser and on mobile, not only from Claude Desktop. It needs a hosted MCP server. Outreach2day's is in early access and has no public URL yet, so this page shows no connector address. When it is generally available, this section will carry the URL and the sign-in steps. Get early access on the home page.

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.co 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

• Rate limits: 10 requests a second and 1,000 an hour per user and per workspace. A 429 carries Retry-After.

• 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.

• Reply text is untrusted. The recent_replies tool returns text written by outsiders. Claude should treat it as data, not instructions.

FAQ

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

Not yet. A custom connector needs a hosted MCP server, and Outreach2day's is in early access. Today Claude Desktop runs a local server over the API.

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?

Not with the local server: it has no send tool. Campaigns run in Outreach2day where enabled for your workspace, or in Instantly or Smartlead after you export mailboxes there.

Related

• Outreach2day MCP for Claude: what the hosted MCP server covers (early access)

• Other assistants: Claude Code, ChatGPT, Grok, Gemini, Cursor, GitHub Copilot, Windsurf, Copilot Studio, Le Chat, n8n

• AI assistants for cold email: every assistant and how it connects

• How to connect ChatGPT to cold email

• Cold email API and pricing

Create an account, add mailboxes, then create a key for Claude.

Get an API key→