How to integrate Mailtrap MCP with LangChain

This guide walks you through connecting Mailtrap to LangChain using the Composio tool router. By the end, you'll have a working Mailtrap agent that can send a test email to marketing team, list all emails sent from mailtrap today, create a new inbox for transactional testing through natural language commands. This guide will help you understand how to give your LangChain agent real control over a Mailtrap account through Composio's Mailtrap MCP server. Before we dive in, let's take a quick look at the key ideas and tools involved.

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Mailtrap

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Mailtrap is an email delivery platform for safe email testing and transactional email sending. It helps you catch bugs and verify email flows without spamming real inboxes.

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Introduction

This guide will help you understand how to give your LangChain agent real control over a Mailtrap account through Composio's Mailtrap MCP server.

Before we dive in, let's take a quick look at the key ideas and tools involved.

Also integrate Mailtrap with

ChatGPT OpenAI Agents SDK Claude Agent SDK Claude Code Claude Cowork Codex OpenCode Cursor VS Code OpenClaw Hermes CLI Google ADK Vercel AI SDK Mastra AI LlamaIndex CrewAI

TL;DR

Here's what you'll learn:

Get and set up your OpenAI and Composio API keys
Connect your Mailtrap project to Composio
Create a Tool Router MCP session for Mailtrap
Initialize an MCP client and retrieve Mailtrap tools
Build a LangChain agent that can interact with Mailtrap
Set up an interactive chat interface for testing

What is LangChain?

LangChain is a framework for developing applications powered by language models. It provides tools and abstractions for building agents that can reason, use tools, and maintain conversation context.

Key features include:

Agent Framework: Build agents that can use tools and make decisions
MCP Integration: Connect to external services through Model Context Protocol adapters
Memory Management: Maintain conversation history across interactions
Multi-Provider Support: Works with OpenAI, Anthropic, and other LLM providers

What is the Mailtrap MCP server, and what's possible with it?

The Mailtrap MCP server is an implementation of the Model Context Protocol that connects your AI agent and assistants like Claude, Cursor, etc directly to your Mailtrap account. It provides structured and secure access so your agent can perform Mailtrap operations on your behalf.

What is the Composio tool router, and how does it fit here?

What is Composio SDK?

Composio's Composio SDK helps agents find the right tools for a task at runtime. You can plug in multiple toolkits (like Gmail, HubSpot, and GitHub), and the agent will identify the relevant app and action to complete multi-step workflows. This can reduce token usage and improve the reliability of tool calls. Read more here: Getting started with Composio SDK

The tool router generates a secure MCP URL that your agents can access to perform actions.

How the Composio SDK works

The Composio SDK follows a three-phase workflow:

Discovery: Searches for tools matching your task and returns relevant toolkits with their details.
Authentication: Checks for active connections. If missing, creates an auth config and returns a connection URL via Auth Link.
Execution: Executes the action using the authenticated connection.

Step-by-step Guide

Step by step10 STEPS

Prerequisites

Before starting this tutorial, make sure you have:

Python 3.10 or higher installed on your system
A Composio account with an API key
An OpenAI API key
Basic familiarity with Python and async programming

Getting API Keys for OpenAI and Composio

OpenAI API Key

Go to the OpenAI dashboard and create an API key. You'll need credits to use the models, or you can connect to another model provider.
Keep the API key safe.

Composio API Key

Log in to the Composio dashboard.
Navigate to your API settings and generate a new API key.
Store this key securely as you'll need it for authentication.

Install dependencies

npm install @composio/langchain @langchain/core @langchain/openai @langchain/mcp-adapters dotenv

Install the required packages for LangChain with MCP support.

What's happening:

@composio/langchain provides Composio integration for LangChain
@langchain/mcp-adapters enables MCP client connections
@langchain/core is the core agent framework
dotenv/config loads environment variables

Set up environment variables

bash

COMPOSIO_API_KEY=your_composio_api_key_here
COMPOSIO_USER_ID=your_composio_user_id_here
OPENAI_API_KEY=your_openai_api_key_here

Create a .env file in your project root.

What's happening:

COMPOSIO_API_KEY authenticates your requests to Composio's API
COMPOSIO_USER_ID identifies the user for session management
OPENAI_API_KEY enables access to OpenAI's language models

Import dependencies

import { Composio } from '@composio/core';
import { LangchainProvider } from '@composio/langchain';
import { MultiServerMCPClient } from "@langchain/mcp-adapters";
import { createAgent } from "langchain";
import * as readline from 'readline';
import 'dotenv/config';

dotenv.config();

What's happening:

We're importing LangChain's MCP adapter and Composio SDK
The dotenv/config import loads environment variables from your .env file
This setup prepares the foundation for connecting LangChain with Mailtrap functionality through MCP

Initialize Composio client

const composioApiKey = process.env.COMPOSIO_API_KEY;
const userId = process.env.COMPOSIO_USER_ID;

if (!composioApiKey) throw new Error('COMPOSIO_API_KEY is not set');
if (!userId) throw new Error('COMPOSIO_USER_ID is not set');

async function main() {
    const composio = new Composio({
        apiKey: composioApiKey as string,
        provider: new LangchainProvider()
    });

What's happening:

We're loading the COMPOSIO_API_KEY from environment variables and validating it exists
Creating a Composio instance that will manage our connection to Mailtrap tools
Validating that COMPOSIO_USER_ID is also set before proceeding

Create a Tool Router session

const session = await composio.create(
    userId as string,
    {
        toolkits: ['mailtrap']
    }
);

const url = session.mcp.url;

What's happening:

We're creating a Tool Router session that gives your agent access to Mailtrap tools
The create method takes the user ID and specifies which toolkits should be available
The returned session.mcp.url is the MCP server URL that your agent will use
This approach allows the agent to dynamically load and use Mailtrap tools as needed

Configure the agent with the MCP URL

const client = new MultiServerMCPClient({
    "mailtrap-agent": {
        transport: "http",
        url: url,
        headers: {
            "x-api-key": process.env.COMPOSIO_API_KEY
        }
    }
});

const tools = await client.getTools();

const agent = createAgent({ model: "gpt-5", tools });

What's happening:

We're creating a MultiServerMCPClient that connects to our Mailtrap MCP server via HTTP
The client is configured with a name and the URL from our Tool Router session
getTools() retrieves all available Mailtrap tools that the agent can use
We're creating a LangChain agent using the GPT-5 model

Set up interactive chat interface

let conversationHistory: any[] = [];

console.log("Chat started! Type 'exit' or 'quit' to end the conversation.\n");
console.log("Ask any Mailtrap related question or task to the agent.\n");

const rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout,
    prompt: 'You: '
});

rl.prompt();

rl.on('line', async (userInput: string) => {
    const trimmedInput = userInput.trim();

    if (['exit', 'quit', 'bye'].includes(trimmedInput.toLowerCase())) {
        console.log("\nGoodbye!");
        rl.close();
        process.exit(0);
    }

    if (!trimmedInput) {
        rl.prompt();
        return;
    }

    conversationHistory.push({ role: "user", content: trimmedInput });
    console.log("\nAgent is thinking...\n");

    const response = await agent.invoke({ messages: conversationHistory });
    conversationHistory = response.messages;

    const finalResponse = response.messages[response.messages.length - 1]?.content;
    console.log(`Agent: ${finalResponse}\n`);
        
        rl.prompt();
    });

    rl.on('close', () => {
        console.log('\n👋 Session ended.');
        process.exit(0);
    });

What's happening:

We initialize an empty conversationHistory list to maintain context across interactions
A readline interface is used to continuously accept user input from the command line
When a user types a message, it's added to the conversation history and sent to the agent
The agent processes the request using the invoke() method with the full conversation history
Users can type 'exit', 'quit', or 'bye' to end the chat session gracefully

Run the application

main().catch((err) => {
    console.error('Fatal error:', err);
    process.exit(1);
});

What's happening:

We call the main() function to start the application

Complete Code

Here's the complete code to get you started with Mailtrap and LangChain:

import { Composio } from '@composio/core';
import { LangchainProvider } from '@composio/langchain';
import { MultiServerMCPClient } from "@langchain/mcp-adapters";  
import { createAgent } from "langchain";
import * as readline from 'readline';
import 'dotenv/config';

const composioApiKey = process.env.COMPOSIO_API_KEY;
const userId = process.env.COMPOSIO_USER_ID;

if (!composioApiKey) throw new Error('COMPOSIO_API_KEY is not set');
if (!userId) throw new Error('COMPOSIO_USER_ID is not set');

async function main() {
    const composio = new Composio({
        apiKey: composioApiKey as string,
        provider: new LangchainProvider()
    });

    const session = await composio.create(
        userId as string,
        {
            toolkits: ['mailtrap']
        }
    );

    const url = session.mcp.url;
    
    const client = new MultiServerMCPClient({
        "mailtrap-agent": {
            transport: "http",
            url: url,
            headers: {
                "x-api-key": process.env.COMPOSIO_API_KEY
            }
        }
    });
    
    const tools = await client.getTools();
  
    const agent = createAgent({ model: "gpt-5", tools });
    
    let conversationHistory: any[] = [];
    
    console.log("Chat started! Type 'exit' or 'quit' to end the conversation.\n");
    console.log("Ask any Mailtrap related question or task to the agent.\n");
    
    const rl = readline.createInterface({
        input: process.stdin,
        output: process.stdout,
        prompt: 'You: '
    });

    rl.prompt();

    rl.on('line', async (userInput: string) => {
        const trimmedInput = userInput.trim();
        
        if (['exit', 'quit', 'bye'].includes(trimmedInput.toLowerCase())) {
            console.log("\nGoodbye!");
            rl.close();
            process.exit(0);
        }
        
        if (!trimmedInput) {
            rl.prompt();
            return;
        }
        
        conversationHistory.push({ role: "user", content: trimmedInput });
        console.log("\nAgent is thinking...\n");
        
        const response = await agent.invoke({ messages: conversationHistory });
        conversationHistory = response.messages;
        
        const finalResponse = response.messages[response.messages.length - 1]?.content;
        console.log(`Agent: ${finalResponse}\n`);
        
        rl.prompt();
    });

    rl.on('close', () => {
        console.log('\nSession ended.');
        process.exit(0);
    });
}

main().catch((err) => {
    console.error('Fatal error:', err);
    process.exit(1);
});

Conclusion

You've successfully built a LangChain agent that can interact with Mailtrap through Composio's Tool Router.

Key features of this implementation:

Dynamic tool loading through Composio's Tool Router
Conversation history maintenance for context-aware responses
Async Python provides clean, efficient execution of agent workflows

You can extend this further by adding error handling, implementing specific business logic, or integrating additional Composio toolkits to create multi-app workflows.

TOOLS

Supported Tools

Every Mailtrap action and event your agent gets out of the box.

Clean Inbox

Tool to clean an inbox in Mailtrap by deleting all messages.

Create Contact

Tool to create a new contact in Mailtrap.

Create Contact Event

Tool to create a contact event in Mailtrap.

Create Contact Export

Tool to create a contact export job for a Mailtrap account.

Create Contact Field

Tool to create a custom contact field in Mailtrap.

Create Contact List

Tool to create a new contact list in Mailtrap.

Create Email Template

Tool to create a new email template in Mailtrap account.

Create Sending Domain

Tool to create a new sending domain in Mailtrap.

Delete Contact

Tool to delete a contact from a Mailtrap account.

Delete Contact Field

Tool to delete a contact field by its ID.

Delete Contact List

Tool to delete a contact list by its ID.

Delete Email Template

Tool to delete an email template from a Mailtrap account.

Delete Project

Tool to delete a project from Mailtrap.

Delete Sending Domain

Tool to delete a sending domain from a Mailtrap account.

Get Billing Usage

Tool to retrieve current billing cycle usage for an account.

Get Contact

Tool to retrieve a contact by UUID or email address from Mailtrap.

Get Contact Export

Tool to retrieve the status of a contact export.

Get Contact Field

Tool to retrieve contact field details by field ID.

Get Contact Import Status

Tool to retrieve the status of a contact import operation.

Get Contact List

Tool to retrieve a specific contact list by its ID.

Get Email Template

Tool to retrieve details of a specific email template by ID.

Get Inbox Attributes

Tool to retrieve inbox attributes from Mailtrap.

Get Message HTML Body

Tool to retrieve the HTML body of a message from Mailtrap.

Get Permission Resources

Tool to retrieve all resources in account for permission management.

Get Project by ID

Tool to retrieve project details from Mailtrap by project ID.

Get Sending Domain

Tool to retrieve sending domain details from Mailtrap.

Get Sending Stats

Tool to retrieve email sending statistics from Mailtrap for a specific account.

Get Sending Stats by Categories

Tool to retrieve email sending statistics grouped by categories.

Get Sending Stats by Date

Tool to retrieve email sending statistics aggregated by date.

Get Sending Stats by Domains

Tool to retrieve sending statistics grouped by domains for a Mailtrap account.

Get Sending Stats by ESP

Tool to retrieve email sending statistics grouped by email service providers (ESPs) for a specified date range.

Import Contacts

Tool to import contacts in bulk to Mailtrap.

List Accounts

Tool to list all Mailtrap accounts you have access to.

List Contact Fields

Tool to get all contact fields for a Mailtrap account.

List Contact Lists

Tool to retrieve all contact lists for a Mailtrap account.

List Email Templates

Tool to retrieve all email templates for a Mailtrap account.

List Inboxes

Tool to get a list of inboxes for a Mailtrap account.

List Messages in Inbox

Tool to get messages from a Mailtrap inbox.

List Projects

Tool to get a list of projects for a Mailtrap account.

List Sending Domains

Tool to list all sending domains for a Mailtrap account.

List Email Suppressions

Tool to list suppressed email addresses for a Mailtrap account.

Mark Inbox as Read

Tool to mark all messages in a Mailtrap inbox as read.

Reset Inbox Credentials

Tool to reset SMTP credentials for a Mailtrap inbox.

Update contact

Tool to update an existing contact in Mailtrap.

Update Contact Field

Tool to update a contact field in Mailtrap.

Update Contact List

Tool to update a contact list's name in Mailtrap.

Update Email Template

Tool to update an existing email template in Mailtrap account.

Update inbox

Tool to update an inbox's settings in Mailtrap.

Update project

Tool to update a project's name in Mailtrap.

FRAMEWORKS

How to build Mailtrap MCP Agent with another framework

ChatGPT

Use Mailtrap MCP with ChatGPT

OpenAI Agents SDK

Use Mailtrap MCP with OpenAI Agents SDK

Claude Agent SDK

Use Mailtrap MCP with Claude Agent SDK

Claude Code

Use Mailtrap MCP with Claude Code

Claude Cowork

Use Mailtrap MCP with Claude Cowork

Codex

Use Mailtrap MCP with Codex

Cursor

Use Mailtrap MCP with Cursor

OpenClaw

Use Mailtrap MCP with OpenClaw

Hermes

Use Mailtrap MCP with Hermes

CLI

Use Mailtrap MCP with CLI

Google ADK

Use Mailtrap MCP with Google ADK

Vercel AI SDK

Use Mailtrap MCP with Vercel AI SDK

Mastra AI

Use Mailtrap MCP with Mastra AI

LlamaIndex

Use Mailtrap MCP with LlamaIndex

CrewAI

Use Mailtrap MCP with CrewAI

OpenCode

Use Mailtrap MCP with OpenCode

VS Code

Use Mailtrap MCP with VS Code

MORE TOOLKITS

Explore Other Toolkits

Toolkit marketplace

Google Sheets

Oauth2

Google Sheets is a cloud-based spreadsheet tool for real-time collaboration and data analysis. It lets teams work together from anywhere, updating information instantly.

Notion

Oauth2Api Key

Notion is a collaborative workspace for notes, docs, wikis, and tasks. It streamlines team knowledge, project tracking, and workflow customization in one place.

Airtable

Oauth2Api Key

Airtable combines the flexibility of spreadsheets with the power of a database for easy project and data management. Teams use Airtable to organize, track, and collaborate with custom views and automations.

Asana

Oauth2

Asana is a collaborative work management platform for teams to organize and track projects. It streamlines teamwork, boosts productivity, and keeps everyone aligned on goals.

FAQ

Frequently asked questions

With a standalone Mailtrap MCP server, the agents and LLMs can only access a fixed set of Mailtrap tools tied to that server. However, with the Composio Tool Router, agents can dynamically load tools from Mailtrap and many other apps based on the task at hand, all through a single MCP endpoint.

Yes, you can. LangChain fully supports MCP integration. You get structured tool calling, message history handling, and model orchestration while Tool Router takes care of discovering and serving the right Mailtrap tools.

Yes, absolutely. You can configure which Mailtrap scopes and actions are allowed when connecting your account to Composio. You can also bring your own OAuth credentials or API configuration so you keep full control over what the agent can do.

All sensitive data such as tokens, keys, and configuration is fully encrypted at rest and in transit. Composio is SOC 2 Type 2 compliant and follows strict security practices so your Mailtrap data and credentials are handled as safely as possible.

Start with Mailtrap.It takes 30 seconds.

Managed auth, hosted MCP servers, and every Mailtrap tool your agent needs.Free to start.

Start building

Customer stories

Teams ship real agents on Composio

GET STARTED FOR FREE BOOK A DEMO

Karan skipped his own birthday party to fix our critical issue. It was 10pm and he diverted his Waymo to help us instead. This really sets the bar — it shows the commitment you need when users rely on your software.

Harsha Gaddipati

Co-founder, Slashy

A lot of students tell us that the moment their connected tools start talking to each other inside Opennote feels almost magical. The agent just knows them, and it's immensely helped keep new users on the platform.

Abhi Arya

Co-founder, Opennote

We chose Composio over Pipedream because it delivered depth where it mattered — niche tools and tricky edge cases other platforms simply ignored. That gave us confidence to scale without compromising.

Nirman Dave

CEO, Zams

As a solo builder, shipping fast is life or death. The only way I can outcompete incumbents is by outmanoeuvring them. Getting bogged down managing agent auth would have been a death sentence.

Ryan Yu

Founder, Extra Thursday

Before Composio, adding tool integrations was slow and resource-intensive. Each one could take weeks of engineering time, and maintaining them meant constantly keeping up with API changes.

Tomisin Jenrola

Founder & CEO, SwarmZero

With hands-on help from their founder, we integrated Gmail and Google Drive in just 30 minutes. This level of personal support and commitment is exactly what startups should strive for.

Jerome Leclanche

Co-Founder, Ingram Technologies

How to integrate Mailtrap MCP with LangChain

Connect Mailtrap without auth hassles

Introduction

Also integrate Mailtrap with

TL;DR

What is LangChain?

What is the Mailtrap MCP server, and what's possible with it?

What is the Composio tool router, and how does it fit here?

What is Composio SDK?

How the Composio SDK works

Step-by-step Guide

Prerequisites

Getting API Keys for OpenAI and Composio

Install dependencies

Set up environment variables

Import dependencies

Initialize Composio client

Create a Tool Router session

Configure the agent with the MCP URL

Set up interactive chat interface

Run the application

Complete Code

Conclusion

Supported Tools

How to build Mailtrap MCP Agent with another framework

ChatGPT

OpenAI Agents SDK

Claude Agent SDK

Claude Code

Claude Cowork

Codex

Cursor

OpenClaw

Hermes

CLI

Google ADK

Vercel AI SDK

Mastra AI

LlamaIndex

CrewAI

OpenCode

VS Code

Explore Other Toolkits

Google Sheets

Notion

Airtable

Asana

Frequently asked questions

What are the differences in Tool Router MCP and Mailtrap MCP?+

Can I use Tool Router MCP with LangChain?+

Can I manage the permissions and scopes for Mailtrap while using Tool Router?+

How safe is my data with Composio Tool Router?+

Start with Mailtrap.It takes 30 seconds.

Teams ship real agents on Composio