How to Connect Copilot Studio to Cold Email

Short answer: Microsoft Copilot Studio agents call outside systems through tools. Two kinds matter here: an MCP server tool, generally available in Copilot Studio since 29 May 2025, and a custom connector built from an OpenAPI definition. The hosted Outreach2day MCP server at https://public.outreach2day.com/mcp signs in with OAuth 2.1 and dynamic client registration, which Copilot Studio's MCP wizard supports as OAuth 2.0 "Dynamic discovery" per Microsoft's docs, so it should connect with a sign-in and no API key; we have not tested it from Copilot Studio yet. The custom connector works with Outreach2day today and is the option when you want a small read-only tool set you define yourself, with an API key. Either gives an agent access to mailboxes, warmup state, domain availability and replies.

Checked September 2026 against Create a custom connector from an OpenAPI definition, Connect your agent to an existing MCP server and Microsoft's MCP general availability announcement.

Connection Methods

The MCP route needs no API key: add a Model Context Protocol tool with the server URL, choose OAuth 2.0, Dynamic discovery, and each user signs in to Outreach2day (steps in Add the Hosted MCP Server). The custom connector below is the REST API route, with a key.

Power Platform data policies apply to both routes: if your admin regulates connectors, the same policy covers an MCP server. On a company tenant, check with the admin before you build.

Add the Hosted MCP Server

The hosted Outreach2day MCP server is live at https://public.outreach2day.com/mcp. In Copilot Studio, open Tools, add a tool, choose Model Context Protocol, enter the URL and choose OAuth 2.0, type Dynamic discovery: Copilot Studio finds our sign-in endpoints and registers itself, and each user signs in to Outreach2day when the connection is created. No API key is needed. For a setup without sign-in, API key auth in a header also works: name Authorization, value Bearer plus an API key from the API keys page. The agent then gets tools for domains, quotes, mailboxes, warmup, campaigns and replies; orders are paid on a Stripe page that you open. We have not tested this from Copilot Studio yet; the custom connector below is the checked route. The tool list is on the MCP page.

Why a Custom Connector Needs Its Own File

Custom connectors accept only OpenAPI 2.0 (Swagger) definitions smaller than 1 MB, per Microsoft's documentation. The Outreach2day spec at https://public.outreach2day.com/openapi.json is OpenAPI 3 and covers well over a hundred operations, so it cannot be imported as is. The short Swagger 2.0 file below describes four read operations. A smaller file is also better for the agent: it chooses between four clear tools instead of a hundred.

The Outreach2day API accepts the key in an x-api-key header as well as Authorization: Bearer. The connector uses x-api-key because Copilot Studio's API key auth sends a named header with the key as its value.

{
  "swagger": "2.0",
  "info": { "title": "Outreach2day", "version": "1.0" },
  "host": "public.outreach2day.com",
  "basePath": "/",
  "schemes": ["https"],
  "produces": ["application/json"],
  "securityDefinitions": {
    "api_key": { "type": "apiKey", "in": "header", "name": "x-api-key" }
  },
  "security": [{ "api_key": [] }],
  "paths": {
    "/workspaces": { "get": {
      "operationId": "ListWorkspaces",
      "summary": "List workspaces the key can see",
      "responses": { "200": { "description": "OK" } } } },
    "/warmup/mailboxes": { "get": {
      "operationId": "WarmupStatus",
      "summary": "Warmup state of every mailbox",
      "parameters": [{ "name": "workspaceId", "in": "query",
        "type": "integer", "required": true }],
      "responses": { "200": { "description": "OK" } } } },
    "/check_domains": { "post": {
      "operationId": "CheckDomains",
      "summary": "Check if domain names are free. Buys nothing.",
      "parameters": [{ "name": "body", "in": "body", "required": true,
        "schema": { "type": "object", "properties": {
          "domains": { "type": "array", "items": { "type": "string" } } } } }],
      "responses": { "200": { "description": "OK" } } } },
    "/threads": { "get": {
      "operationId": "ListReplies",
      "summary": "Reply threads with a reply intent label",
      "parameters": [
        { "name": "workspaceId", "in": "query", "type": "integer", "required": true },
        { "name": "hasCustomerReply", "in": "query", "type": "boolean" },
        { "name": "limit", "in": "query", "type": "integer" }],
      "responses": { "200": { "description": "OK" } } } }
  }
}

The responses are left untyped to keep the file short. Copilot Studio still passes the JSON to the agent; add response schemas later if you want typed outputs in Power Automate.

Connect a Custom Connector on the REST API, step by step

1. Create an API key. In the Outreach2day app, open the API keys page and create a key only for this agent, so you can revoke it on its own

2. Save the definition. Save the JSON above as outreach2day.json

3. Create the custom connector. In Power Apps or Power Automate, open Solutions, pick or create a solution, then New, Automation, Custom connector, and "Import an OpenAPI file". Select the file and create the connector. On the Security page, check that auth is API key, parameter x-api-key, location Header

4. Test it. On the Test page, create a connection with your API key from the API keys page and run ListWorkspaces. Wait a few minutes after creating the connector before testing, as Microsoft recommends for API key connectors

5. Add it to the agent. In Copilot Studio, open the agent's Tools page, add a tool and pick the connector's operations. Describe each tool in plain words ("use WarmupStatus to answer questions about warmup") and give the agent your workspace ID in its instructions

6. Try it in the test pane. Ask "Which mailboxes are still warming?" and compare the answer with the app

Prompts to Try With the Agent

• "Which mailboxes are still warming, and when did each start?"

• "Are acmemail.com, tryacme.com and acme-mail.com free? Do not buy."

• "List today's replies marked interested or meeting_request with the lead's email."

• "How many mailboxes are paused or in error?"

Keep sending rules in the agent's instructions so drafts follow them: at most 25 cold emails per mailbox a day, 5 mailboxes per domain, 14 days of warmup before cold email, no links, follow-ups after 2, 3, 5 and 5 days.

Limits and Safety

• Read-only by design. The file has no purchase or send operation. Buying domains through the API is paid right away — give an agent a billing-scoped key only if you want it to buy.

• Shared connections. Decide whether agent users bring their own key or share one. A shared key acts as one Outreach2day user for everyone.

• API limits and key safety: cold email API.

FAQ

Can I import the Outreach2day OpenAPI spec directly?

No. Custom connectors take OpenAPI 2.0 files under 1 MB, and the Outreach2day spec is OpenAPI 3 and larger. Use the short Swagger 2.0 file on this page.

Does Copilot Studio support MCP servers with an API key?

Yes. Its MCP wizard offers OAuth 2.0 (dynamic discovery, dynamic or manual), API key authentication in a header or a query parameter, and no auth. The Outreach2day server works with OAuth dynamic discovery, so no key is needed; the key header is a fallback. Only the Streamable HTTP transport is supported.

Is this the same as GitHub Copilot?

No. GitHub Copilot is a coding assistant in editors such as VS Code; see how to connect GitHub Copilot to cold email.

Can the agent send cold emails?

Not with this connector.

What does API access cost?

Nothing extra: it is part of every Outreach2day plan. Copilot Studio has its own Microsoft licensing. See our pricing.

Related

Create an account and add mailboxes, then add the MCP server tool and sign in; for the custom connector, create a key on the API keys page.