Build Email Agents with Claude's Native Tool Use

Connect Anthropic's Claude API to MultiMail and let your agents send, read, and manage email — with configurable human oversight at every step.

Anthropic's Claude API provides native tool use capabilities that map directly to MultiMail's email tools. Claude can call structured tools like send_email, check_inbox, and reply_email with well-formed JSON arguments, making it a natural fit for building email agents that interact with real mailboxes.

By integrating MultiMail with the Claude API, your agents gain full email capabilities while respecting human oversight boundaries. The default gated_send mode means Claude drafts emails but a human approves before delivery, creating a trust ladder that lets you safely increase agent autonomy over time.

You can connect Claude to MultiMail by defining email tools in Claude's tool use format and calling the MultiMail REST API, or by connecting to the @multimail/mcp-server for automatic tool discovery. Both approaches give your agent structured access to the full suite of email operations.

Why MultiMail

Built for Anthropic Claude API developers

Native Tool Use Alignment

Claude's tool_use feature accepts structured JSON tool definitions. MultiMail's email tools map directly to this format — send_email, check_inbox, reply_email — with typed parameters that Claude fills reliably.

Graduated Trust via Oversight Modes

Start with gated_send (Claude composes, human approves) and progress to monitored or autonomous as trust builds. MultiMail supports five oversight modes so you can match the level of autonomy to your confidence in the agent.

MCP Server Integration

The @multimail/mcp-server package exposes email tools in the Model Context Protocol format. Claude's MCP support lets your agent discover and call all MultiMail tools without manual tool definitions.

Thread-Aware Conversations

MultiMail tracks email threads automatically. Your Claude agent can retrieve full conversation history with get_thread, enabling context-aware replies that maintain continuity across multi-turn email exchanges.

Structured Output Reliability

Claude excels at generating well-structured JSON tool calls. Combined with MultiMail's typed API, this means fewer malformed requests and more reliable email agent workflows compared to free-form API calls.

Try it

Try it with your agent

No code, no dashboard. Paste this to your AI agent — it connects MultiMail, creates an inbox, and builds the flow for you.

You are my implementation agent for connecting Anthropic Claude API to MultiMail. Complete these steps without inventing APIs, endpoints, headers, or webhooks. 1. Get MultiMail ready: read https://multimail.dev/llms.txt, follow its MCP server connection instructions, create a free MultiMail inbox, and set up a verified sending domain for outbound mail. 2. Wire Claude through Anthropic Claude API tool use: use the Messages API with Anthropic client tools, define tools that call the connected MultiMail MCP server from my application runtime, and handle Claude tool_use requests by executing the matching MCP-backed operation and returning tool_result content to Claude. 3. Give the agent three capabilities only: check the inbox for new and relevant messages, draft replies for review, and send or schedule email through MultiMail. Keep all MultiMail actions behind the MCP server instructions from llms.txt. 4. Send a test email: have Claude check the inbox, draft a short reply or outbound test message, show me the exact recipient, subject, and body, then use the MultiMail send capability only after I approve. 5. Run with oversight mode gated_send: configure MultiMail so every outbound send or scheduled send requires my review before release. Do not switch to monitored or autonomous until I explicitly ask.
Getting started

Step by step

1

Create a MultiMail Account and API Key

Sign up at multimail.dev, create a mailbox, and generate an API key from your dashboard. Your key will start with mm_live_.

2

Install the Anthropic SDK

Install the Anthropic Python SDK and requests library for calling the MultiMail API.

3

Define Email Tool Schemas

Create tool definitions for send_email, check_inbox, and other MultiMail operations using Claude's input_schema format.

4

Build the Agent Loop

Implement a loop that sends messages to Claude, detects tool_use stop reasons, executes tools against MultiMail, and returns results.

5

Approve Pending Emails

If your mailbox uses gated_send mode (the default), review and approve pending emails in the MultiMail dashboard before they are delivered.

FAQ

Common questions

Does Claude have a native MultiMail integration?
There is no built-in MultiMail integration in the Anthropic SDK. You integrate MultiMail by defining custom tools with JSON schemas that Claude calls via its tool_use feature, then executing those calls against the MultiMail REST API. Alternatively, you can use the @multimail/mcp-server with Claude's MCP support for automatic tool discovery.
What happens when Claude sends an email in gated_send mode?
In gated_send mode, the MultiMail API returns a success response with a pending status. The email is queued for human review in the MultiMail dashboard. Once approved, it is delivered. Claude can check the status of pending emails using the list_pending endpoint.
How does Claude's tool use compare to other providers for email agents?
Claude's tool use produces highly reliable structured outputs with well-formed JSON arguments. This means fewer malformed email API calls compared to models that struggle with complex parameter schemas. Claude also follows system prompt instructions about oversight modes consistently, making it well-suited for email agent use cases.
Can I use Claude's streaming with MultiMail tools?
Yes. Claude's streaming API works with tool use. You receive real-time text output and tool call events as they happen, so your UI can show progress while the agent processes email tasks. Tool execution happens between stream segments.
Is there rate limiting on the MultiMail API?
Rate limits depend on your plan tier. The Starter (free) plan allows 200 emails per month, while paid plans range from 5,000 to 150,000. The API returns standard 429 responses when limits are reached, which your agent loop can handle with retry logic.
Related integrations

Explore more

LangChain

orchestration · both

View guide →

Vercel AI SDK

tool-use · typescript

View guide →

OpenAI API

tool-use · both

View guide →
Get started

The only agent email with a verifiable sender

Email infrastructure built for AI agents. Verifiable identity, graduated oversight, and a hosted MCP server. Formally verified in Lean 4.

Read the Docs →See Pricing