How to integrate Postmark MCP with Claude Agent SDK

This guide walks you through connecting Postmark to the Claude Agent SDK using the Composio tool router. By the end, you'll have a working Postmark agent that can send a password reset email to user, get delivery status for last 10 emails, list all bounced emails from today through natural language commands. This guide will help you understand how to give your Claude Agent SDK agent real control over a Postmark account through Composio's Postmark MCP server. Before we dive in, let's take a quick look at the key ideas and tools involved.

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Postmark is an email delivery service for sending transactional emails with reliable deliverability. It delivers detailed analytics and fast, secure email delivery for developers.

46 Tools

Introduction

This guide walks you through connecting Postmark to the Claude Agent SDK using the Composio tool router. By the end, you'll have a working Postmark agent that can send a password reset email to user, get delivery status for last 10 emails, list all bounced emails from today through natural language commands.

This guide will help you understand how to give your Claude Agent SDK agent real control over a Postmark account through Composio's Postmark MCP server.

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

Also integrate Postmark with

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TL;DR

Here's what you'll learn:
  • Get and set up your Claude/Anthropic and Composio API keys
  • Install the necessary dependencies
  • Initialize Composio and create a Tool Router session for Postmark
  • Configure an AI agent that can use Postmark as a tool
  • Run a live chat session where you can ask the agent to perform Postmark operations

What is Claude Agent SDK?

The Claude Agent SDK is Anthropic's official framework for building AI agents powered by Claude. It provides a streamlined interface for creating agents with MCP tool support and conversation management.

Key features include:

  • Native MCP Support: Built-in support for Model Context Protocol servers
  • Permission Modes: Control tool execution permissions
  • Streaming Responses: Real-time response streaming for interactive applications
  • Context Manager: Clean async context management for sessions

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

The Postmark MCP server is an implementation of the Model Context Protocol that connects your AI agent and assistants like Claude, Cursor, etc directly to your Postmark account. It provides structured and secure access to transactional email sending and analytics, so your agent can perform actions like delivering transactional emails, monitoring delivery status, managing templates, and analyzing engagement metrics on your behalf.

  • Automated transactional email delivery: Let your agent send password resets, confirmations, and notification emails with high deliverability and reliability.
  • Template management and customization: Enable your agent to create, update, or select dynamic email templates for consistent, branded communications.
  • Email delivery status monitoring: Ask your agent to track sent messages, check delivery receipts, and identify bounced or failed emails in real time.
  • Engagement and analytics tracking: Have your agent retrieve open and click data, analyze engagement trends, and provide actionable insights from your email campaigns.
  • Suppression list and recipient management: Direct your agent to manage suppression lists, process unsubscribes, and maintain healthy recipient lists automatically.

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:
  • Composio API Key and Claude/Anthropic API Key
  • Primary know-how of Claude Agents SDK
  • A Postmark account
  • Some knowledge of Python
2

Getting API Keys for Claude/Anthropic and Composio

Claude/Anthropic API Key
  • Go to the Anthropic Console and create an API key. You'll need credits to use the models.
  • 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.
3

Install dependencies

npm install @anthropic-ai/claude-agent-sdk @composio/core dotenv

Install the Composio SDK and the Claude Agents SDK.

What's happening:

  • @composio/core provides Composio integration for Anthropic
  • @anthropic-ai/claude-agent-sdk is the core agent framework
  • dotenv/config loads environment variables
4

Set up environment variables

bash
COMPOSIO_API_KEY=your_composio_api_key_here
USER_ID=your_user_id_here
ANTHROPIC_API_KEY=your_anthropic_api_key_here

Create a .env file in your project root.

What's happening:

  • COMPOSIO_API_KEY authenticates with Composio
  • USER_ID identifies the user for session management
  • ANTHROPIC_API_KEY authenticates with Anthropic/Claude
5

Import dependencies

import 'dotenv/config';
import readline from 'node:readline';
import { Composio } from '@composio/core';
import { query, type Options } from "@anthropic-ai/claude-agent-sdk";

dotenv.config();
What's happening:
  • We're importing all necessary libraries including the Claude Agent SDK and Composio
  • The dotenv.config() function loads environment variables from your .env file
  • This setup prepares the foundation for connecting Claude with Postmark functionality
6

Create a Composio instance and Tool Router session

async function chat() {
  const { COMPOSIO_API_KEY, USER_ID } = process.env;
  if (!COMPOSIO_API_KEY || !USER_ID) {
    throw new Error('COMPOSIO_API_KEY and USER_ID required in .env');
  }

  const composio = new Composio({ apiKey: COMPOSIO_API_KEY });

  // Create Tool Router session for Postmark
  const session = await composio.create(USER_ID, {
    toolkits: ['postmark'],
  });
  const mcpUrl = session?.mcp.url;
What's happening:
  • The function checks for the required COMPOSIO_API_KEY environment variable
  • We're creating a Composio instance using our API key
  • The create method creates a Tool Router session for Postmark
  • The returned url is the MCP server URL that your agent will use
7

Configure Claude Agent with MCP

const options: Options = {
  permissionMode: 'bypassPermissions',
  mcpServers: {
    composio: {
      type: 'http',
      url: mcpUrl,
      headers: { 'x-api-key': COMPOSIO_API_KEY }
    }
  },
  systemPrompt: 'You are a helpful assistant with access to Postmark tools via Composio.',
  maxTurns: 10,
};
What's happening:
  • We're configuring the Claude Agent options with the MCP server URL
  • permissionMode: 'bypassPermissions' allows the agent to execute operations without asking for permission each time
  • The system prompt instructs the agent that it has access to Postmark
  • maxTurns: 10 limits the conversation length to prevent excessive API usage
8

Create client and start chat loop

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

  console.log('\nChat started. Type "exit" to quit.\n');

  let isProcessing = false;

  async function ask(prompt: string) {
    isProcessing = true;
    rl.pause();

    process.stdout.write('Claude is thinking...');
    const stream = query({ prompt, options });

    let firstChunk = true;
    for await (const msg of stream) {
      const content = (msg as any).message?.content || (msg as any).content;
      if (Array.isArray(content)) {
        for (const block of content) {
          if (block.type === 'text' && block.text) {
            if (firstChunk) {
              process.stdout.write('\r\x1b[K');
              process.stdout.write('Claude: ');
              firstChunk = false;
            }
            process.stdout.write(block.text);
          }
        }
      }
    }
    process.stdout.write('\n\n');

    isProcessing = false;
    rl.resume();
    rl.prompt();
  }

  rl.on('line', async (line) => {
    if (isProcessing) return;

    const input = line.trim();
    if (input === 'exit') {
      rl.close();
      process.exit(0);
    }
    if (input) await ask(input);
    else rl.prompt();
  });

  await ask('What can you help me with?');
}
What's happening:
  • The readline interface is created to handle user input and output
  • The query function is used to send the user's input to the agent
  • The chat loop continues until the user types 'exit' or 'quit'
9

Run the application

try {
  await chat();
} catch (error) {
  console.error(error);
  process.exit(1);
}
What's happening:
  • The chat function is the entry point for the application
  • The try-catch block is used to handle any errors that occur

Complete Code

Here's the complete code to get you started with Postmark and Claude Agent SDK:

import 'dotenv/config';
import readline from 'node:readline';
import { Composio } from '@composio/core';
import { query, type Options } from "@anthropic-ai/claude-agent-sdk";

async function chat() {
  const { COMPOSIO_API_KEY, USER_ID } = process.env;
  if (!COMPOSIO_API_KEY || !USER_ID) {
    throw new Error('COMPOSIO_API_KEY and USER_ID required in .env');
  }

  const composio = new Composio({ apiKey: COMPOSIO_API_KEY });
  const session = await composio.create(USER_ID, {
    toolkits: ['postmark']
  });
  const mcp_url = session?.mcp.url;

  const options: Options = {
    permissionMode: 'bypassPermissions',
    mcpServers: {
      composio: {
        type: 'http',
        url: mcp_url,
        headers: { 'x-api-key': COMPOSIO_API_KEY }
      }
    },
    systemPrompt: 'You are a helpful assistant with access to Postmark tools via Composio.',
    maxTurns: 10,
  };

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

  console.log('\nChat started. Type "exit" to quit.\n');

  let isProcessing = false;

  async function ask(prompt: string) {
    isProcessing = true;
    rl.pause();

    process.stdout.write('Claude is thinking...');
    const stream = query({ prompt, options });

    let firstChunk = true;
    for await (const msg of stream) {
      const content = (msg as any).message?.content || (msg as any).content;
      if (Array.isArray(content)) {
        for (const block of content) {
          if (block.type === 'text' && block.text) {
            if (firstChunk) {
              process.stdout.write('\r\x1b[K');
              process.stdout.write('Claude: ');
              firstChunk = false;
            }
            process.stdout.write(block.text);
          }
        }
      }
    }
    process.stdout.write('\n\n');

    isProcessing = false;
    rl.resume();
    rl.prompt();
  }

  rl.on('line', async (line) => {
    if (isProcessing) return;

    const input = line.trim();
    if (input === 'exit') {
      rl.close();
      process.exit(0);
    }
    if (input) await ask(input);
    else rl.prompt();
  });

  await ask('What can you help me with?');
}

try {
  await chat();
} catch (error) {
  console.error(error);
  process.exit(1);
}

Conclusion

You've successfully built a Claude Agent SDK agent that can interact with Postmark through Composio's Tool Router.

Key features:

  • Native MCP support through Claude's agent framework
  • Streaming responses for real-time interaction
  • Permission bypass for smooth automated workflows
You can extend this by adding more toolkits, implementing custom business logic, or building a web interface around the agent.
TOOLS

Supported Tools

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

Archive Message Stream

Tool to archive a message stream (soft delete).

Check Spam Score

Tool to assess the spam score of a raw email via the SpamCheck API.

Create Inbound Rule

Tool to create a new inbound rule trigger to block email from a specific sender or domain.

Create Message Stream

Tool to create a new message stream.

Create Suppressions

Tool to add email addresses to the suppression list for a message stream.

Create Template

Tool to create a new email template.

Create Webhook

Tool to create a new webhook configuration for Postmark.

Delete Inbound Rule

Tool to delete a specific inbound rule trigger.

Delete Suppressions

Tool to remove email addresses from the suppression list for a message stream.

Delete Template

Tool to delete a template by its ID or alias.

Delete Webhook

Tool to delete a specific webhook.

Edit Server

Tool to update settings for the current Postmark server.

Edit Template

Tool to update an existing Postmark template by its ID.

Edit Webhook

Tool to update an existing webhook’s URL or triggers.

Get Bounce Counts

Tool to get total counts of emails that have been returned as bounced.

Get Bounces

Tool to retrieve a list of bounces for a server with optional filters.

Get Browser Platform Usage

Tool to retrieve browser platform usage statistics for clicked links.

Get Browser Usage

Tool to retrieve browser usage statistics for clicked links.

Get Click Counts

Tool to retrieve total click counts across all links in emails.

Get Clicks By Browser Family

Tool to retrieve click statistics grouped by browser family.

Get Clicks by Location

Tool to get an overview of which part of the email links were clicked from (HTML or Text).

Get Delivery Stats

Tool to retrieve delivery statistics.

Get Email Client Usage

Tool to retrieve statistics on email clients used to open emails.

Get Email Open Counts

Tool to retrieve counts of opened emails.

Get Message Stream

Tool to retrieve details of a specific message stream by its ID.

Get Opens by Platform

Tool to retrieve email open statistics by platform type.

Get Outbound Overview

Tool to retrieve outbound email statistics overview.

Get Sent Counts

Tool to retrieve total count of emails sent out.

Get Server

Tool to retrieve details of the current Postmark server.

Get Spam Complaints

Tool to retrieve counts of spam complaints.

Get Template

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

Get Tracked Email Counts

Tool to retrieve counts of emails with tracking enabled.

Get Webhook

Tool to retrieve details of a specific webhook by its ID.

List Inbound Rules

Tool to list all inbound rules (triggers) configured for blocking senders.

List Message Streams

Tool to list all message streams for a Postmark server with optional type and archive filtering.

List Outbound Message Clicks

Tool to list clicks for outbound messages with filtering options.

List Outbound Message Opens

Tool to retrieve opens for outbound messages with filtering options.

List Suppressions

Tool to retrieve the suppression list for a message stream with optional filtering.

List Templates

Tool to list all templates for a Postmark server.

List Webhooks

Tool to list all webhooks configured for your Postmark account.

Search Inbound Messages

Tool to search inbound messages received with optional filtering.

Search Outbound Messages

Tool to search outbound messages with filtering by recipient, tag, status, and date range.

Send Batch Templated Emails

Tool to send multiple templated emails in a single batch API call.

Unarchive Message Stream

Tool to unarchive a previously archived message stream.

Update Message Stream

Tool to update a message stream configuration in Postmark.

Validate Template

Tool to validate a Postmark template.

FRAMEWORKS

How to build Postmark MCP Agent with another framework

OpenAI Agents SDK logo

OpenAI Agents SDK

Use Postmark MCP with OpenAI Agents SDK

Claude Code logo

Claude Code

Use Postmark MCP with Claude Code

Claude Cowork logo

Claude Cowork

Use Postmark MCP with Claude Cowork

Codex logo

Codex

Use Postmark MCP with Codex

OpenClaw logo

OpenClaw

Use Postmark MCP with OpenClaw

Hermes logo

Hermes

Use Postmark MCP with Hermes

CLI logo

CLI

Use Postmark MCP with CLI

Google ADK logo

Google ADK

Use Postmark MCP with Google ADK

LangChain logo

LangChain

Use Postmark MCP with LangChain

Vercel AI SDK logo

Vercel AI SDK

Use Postmark MCP with Vercel AI SDK

Mastra AI logo

Mastra AI

Use Postmark MCP with Mastra AI

LlamaIndex logo

LlamaIndex

Use Postmark MCP with LlamaIndex

CrewAI logo

CrewAI

Use Postmark MCP with CrewAI

FAQ

Frequently asked questions

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

Yes, you can. Claude Agent SDK 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 Postmark tools.

Yes, absolutely. You can configure which Postmark 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 Postmark data and credentials are handled as safely as possible.

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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.

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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.

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