How to integrate Mailtrap MCP with Mastra AI

This guide walks you through connecting Mailtrap to Mastra AI 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 Mastra AI 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 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.

49 Tools

Introduction

This guide walks you through connecting Mailtrap to Mastra AI 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 Mastra AI 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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TL;DR

Here's what you'll learn:
  • Set up your environment so Mastra, OpenAI, and Composio work together
  • Create a Tool Router session in Composio that exposes Mailtrap tools
  • Connect Mastra's MCP client to the Composio generated MCP URL
  • Fetch Mailtrap tool definitions and attach them as a toolset
  • Build a Mastra agent that can reason, call tools, and return structured results
  • Run an interactive CLI where you can chat with your Mailtrap agent

What is Mastra AI?

Mastra AI is a TypeScript framework for building AI agents with tool support. It provides a clean API for creating agents that can use external services through MCP.

Key features include:

  • MCP Client: Built-in support for Model Context Protocol servers
  • Toolsets: Organize tools into logical groups
  • Step Callbacks: Monitor and debug agent execution
  • OpenAI Integration: Works with OpenAI models via @ai-sdk/openai

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:

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

Step-by-step Guide

Step by step09 STEPS
1

Prerequisites

Before starting, make sure you have:
  • Node.js 18 or higher
  • A Composio account with an active API key
  • An OpenAI API key
  • Basic familiarity with TypeScript
2

Getting API Keys for OpenAI and Composio

OpenAI API Key
  • Go to the OpenAI dashboard and create an API key.
  • You need credits or a connected billing setup to use the models.
  • Store the key somewhere safe.
Composio API Key
  • Log in to the Composio dashboard.
  • Go to Settings and copy your API key.
  • This key lets your Mastra agent talk to Composio and reach Mailtrap through MCP.
3

Install dependencies

bash
npm install @composio/core @mastra/core @mastra/mcp @ai-sdk/openai dotenv

Install the required packages.

What's happening:

  • @composio/core is the Composio SDK for creating MCP sessions
  • @mastra/core provides the Agent class
  • @mastra/mcp is Mastra's MCP client
  • @ai-sdk/openai is the model wrapper for OpenAI
  • dotenv loads environment variables from .env
4

Set up environment variables

bash
COMPOSIO_API_KEY=your_composio_api_key_here
COMPOSIO_USER_ID=your_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
  • COMPOSIO_USER_ID tells Composio which user this session belongs to
  • OPENAI_API_KEY lets the Mastra agent call OpenAI models
5

Import libraries and validate environment

typescript
import "dotenv/config";
import { openai } from "@ai-sdk/openai";
import { Agent } from "@mastra/core/agent";
import { MCPClient } from "@mastra/mcp";
import { Composio } from "@composio/core";
import * as readline from "readline";

import type { AiMessageType } from "@mastra/core/agent";

const openaiAPIKey = process.env.OPENAI_API_KEY;
const composioAPIKey = process.env.COMPOSIO_API_KEY;
const composioUserID = process.env.COMPOSIO_USER_ID;

if (!openaiAPIKey) throw new Error("OPENAI_API_KEY is not set");
if (!composioAPIKey) throw new Error("COMPOSIO_API_KEY is not set");
if (!composioUserID) throw new Error("COMPOSIO_USER_ID is not set");

const composio = new Composio({
  apiKey: composioAPIKey as string,
});
What's happening:
  • dotenv/config auto loads your .env so process.env.* is available
  • openai gives you a Mastra compatible model wrapper
  • Agent is the Mastra agent that will call tools and produce answers
  • MCPClient connects Mastra to your Composio MCP server
  • Composio is used to create a Tool Router session
6

Create a Tool Router session for Mailtrap

typescript
async function main() {
  const session = await composio.create(
    composioUserID as string,
    {
      toolkits: ["mailtrap"],
    },
  );

  const composioMCPUrl = session.mcp.url;
  console.log("Mailtrap MCP URL:", composioMCPUrl);
What's happening:
  • create spins up a short-lived MCP HTTP endpoint for this user
  • The toolkits array contains "mailtrap" for Mailtrap access
  • session.mcp.url is the MCP URL that Mastra's MCPClient will connect to
7

Configure Mastra MCP client and fetch tools

typescript
const mcpClient = new MCPClient({
    id: composioUserID as string,
    servers: {
      nasdaq: {
        url: new URL(composioMCPUrl),
        requestInit: {
          headers: session.mcp.headers,
        },
      },
    },
    timeout: 30_000,
  });

console.log("Fetching MCP tools from Composio...");
const composioTools = await mcpClient.getTools();
console.log("Number of tools:", Object.keys(composioTools).length);
What's happening:
  • MCPClient takes an id for this client and a list of MCP servers
  • The headers property includes the x-api-key for authentication
  • getTools fetches the tool definitions exposed by the Mailtrap toolkit
8

Create the Mastra agent

typescript
const agent = new Agent({
    name: "mailtrap-mastra-agent",
    instructions: "You are an AI agent with Mailtrap tools via Composio.",
    model: "openai/gpt-5",
  });
What's happening:
  • Agent is the core Mastra agent
  • name is just an identifier for logging and debugging
  • instructions guide the agent to use tools instead of only answering in natural language
  • model uses openai("gpt-5") to configure the underlying LLM
9

Set up interactive chat interface

typescript
let messages: AiMessageType[] = [];

console.log("Chat started! Type 'exit' or 'quit' to end.\n");

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

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;
  }

  messages.push({
    id: crypto.randomUUID(),
    role: "user",
    content: trimmedInput,
  });

  console.log("\nAgent is thinking...\n");

  try {
    const response = await agent.generate(messages, {
      toolsets: {
        mailtrap: composioTools,
      },
      maxSteps: 8,
    });

    const { text } = response;

    if (text && text.trim().length > 0) {
      console.log(`Agent: ${text}\n`);
        messages.push({
          id: crypto.randomUUID(),
          role: "assistant",
          content: text,
        });
      }
    } catch (error) {
      console.error("\nError:", error);
    }

    rl.prompt();
  });

  rl.on("close", async () => {
    console.log("\nSession ended.");
    await mcpClient.disconnect();
    process.exit(0);
  });
}

main().catch((err) => {
  console.error("Fatal error:", err);
  process.exit(1);
});
What's happening:
  • messages keeps the full conversation history in Mastra's expected format
  • agent.generate runs the agent with conversation history and Mailtrap toolsets
  • maxSteps limits how many tool calls the agent can take in a single run
  • onStepFinish is a hook that prints intermediate steps for debugging

Complete Code

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

typescript
import "dotenv/config";
import { openai } from "@ai-sdk/openai";
import { Agent } from "@mastra/core/agent";
import { MCPClient } from "@mastra/mcp";
import { Composio } from "@composio/core";
import * as readline from "readline";

import type { AiMessageType } from "@mastra/core/agent";

const openaiAPIKey = process.env.OPENAI_API_KEY;
const composioAPIKey = process.env.COMPOSIO_API_KEY;
const composioUserID = process.env.COMPOSIO_USER_ID;

if (!openaiAPIKey) throw new Error("OPENAI_API_KEY is not set");
if (!composioAPIKey) throw new Error("COMPOSIO_API_KEY is not set");
if (!composioUserID) throw new Error("COMPOSIO_USER_ID is not set");

const composio = new Composio({ apiKey: composioAPIKey as string });

async function main() {
  const session = await composio.create(composioUserID as string, {
    toolkits: ["mailtrap"],
  });

  const composioMCPUrl = session.mcp.url;

  const mcpClient = new MCPClient({
    id: composioUserID as string,
    servers: {
      mailtrap: {
        url: new URL(composioMCPUrl),
        requestInit: {
          headers: session.mcp.headers,
        },
      },
    },
    timeout: 30_000,
  });

  const composioTools = await mcpClient.getTools();

  const agent = new Agent({
    name: "mailtrap-mastra-agent",
    instructions: "You are an AI agent with Mailtrap tools via Composio.",
    model: "openai/gpt-5",
  });

  let messages: AiMessageType[] = [];

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

  rl.prompt();

  rl.on("line", async (input: string) => {
    const trimmed = input.trim();
    if (["exit", "quit"].includes(trimmed.toLowerCase())) {
      rl.close();
      return;
    }

    messages.push({ id: crypto.randomUUID(), role: "user", content: trimmed });

    const { text } = await agent.generate(messages, {
      toolsets: { mailtrap: composioTools },
      maxSteps: 8,
    });

    if (text) {
      console.log(`Agent: ${text}\n`);
      messages.push({ id: crypto.randomUUID(), role: "assistant", content: text });
    }

    rl.prompt();
  });

  rl.on("close", async () => {
    await mcpClient.disconnect();
    process.exit(0);
  });
}

main();

Conclusion

You've built a Mastra AI agent that can interact with Mailtrap through Composio's Tool Router. You can extend this further by:
  • Adding other toolkits like Gmail, Slack, or GitHub
  • Building a web-based chat interface around this agent
  • Using multiple MCP endpoints to enable cross-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.

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. Mastra AI 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.

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