How to integrate Postmark MCP with Google ADK

This guide walks you through connecting Postmark to Google ADK 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 Google ADK 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

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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.

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Introduction

This guide will help you understand how to give your Google ADK 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

OpenAI Agents SDK Claude Agent SDK Claude Code Claude Cowork Codex OpenClaw Hermes CLI LangChain Vercel AI SDK Mastra AI LlamaIndex CrewAI

TL;DR

Here's what you'll learn:

Get a Postmark account set up and connected to Composio
Install the Google ADK and Composio packages
Create a Composio Tool Router session for Postmark
Build an agent that connects to Postmark through MCP
Interact with Postmark using natural language

What is Google ADK?

Google ADK (Agents Development Kit) is Google's framework for building AI agents powered by Gemini models. It provides tools for creating agents that can use external services through the Model Context Protocol.

Key features include:

Gemini Integration: Native support for Google's Gemini models
MCP Toolset: Built-in support for Model Context Protocol tools
Streamable HTTP: Connect to external services through streamable HTTP
CLI and Web UI: Run agents via command line or web interface

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:

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 step09 STEPS

Prerequisites

Before starting, make sure you have:

A Google API key for Gemini models
A Composio account and API key
Python 3.9 or later installed
Basic familiarity with Python

Getting API Keys for Google and Composio

Google API Key

Go to Google AI Studio and create an API key.
Copy the key and keep it safe. You will put this in GOOGLE_API_KEY.

Composio API Key and User ID

Log in to the Composio dashboard.
Go to Settings → API Keys and copy your Composio API key. Use this for COMPOSIO_API_KEY.
Decide on a stable user identifier to scope sessions, often your email or a user ID. Use this for COMPOSIO_USER_ID.

Install dependencies

bash

pip install google-adk composio python-dotenv

Inside your virtual environment, install the required packages.

What's happening:

google-adk is Google's Agents Development Kit
composio connects your agent to Postmark via MCP
python-dotenv loads environment variables

Set up ADK project

bash

adk create my_agent

Set up a new Google ADK project.

What's happening:

This creates an agent folder with a root agent file and .env file

Set environment variables

bash

GOOGLE_API_KEY=your-google-api-key
COMPOSIO_API_KEY=your-composio-api-key
COMPOSIO_USER_ID=your-user-id-or-email

Save all your credentials in the .env file.

What's happening:

GOOGLE_API_KEY authenticates with Google's Gemini models
COMPOSIO_API_KEY authenticates with Composio
COMPOSIO_USER_ID identifies the user for session management

Import modules and validate environment

python

import os
import warnings

from composio import Composio
from dotenv import load_dotenv
from google.adk.agents.llm_agent import Agent
from google.adk.tools.mcp_tool.mcp_session_manager import StreamableHTTPConnectionParams
from google.adk.tools.mcp_tool.mcp_toolset import McpToolset

load_dotenv()

warnings.filterwarnings("ignore", message=".*BaseAuthenticatedTool.*")

GOOGLE_API_KEY = os.getenv("GOOGLE_API_KEY")
COMPOSIO_API_KEY = os.getenv("COMPOSIO_API_KEY")
COMPOSIO_USER_ID = os.getenv("COMPOSIO_USER_ID")

if not GOOGLE_API_KEY:
    raise ValueError("GOOGLE_API_KEY is not set in the environment.")
if not COMPOSIO_API_KEY:
    raise ValueError("COMPOSIO_API_KEY is not set in the environment.")
if not COMPOSIO_USER_ID:
    raise ValueError("COMPOSIO_USER_ID is not set in the environment.")

What's happening:

os reads environment variables
Composio is the main Composio SDK client
GoogleProvider declares that you are using Google ADK as the agent runtime
Agent is the Google ADK LLM agent class
McpToolset lets the ADK agent call MCP tools over HTTP

Create Composio client and Tool Router session

python

composio_client = Composio(api_key=COMPOSIO_API_KEY)

composio_session = composio_client.create(
    user_id=COMPOSIO_USER_ID,
    toolkits=["postmark"],
)

COMPOSIO_MCP_URL = composio_session.mcp.url,
print(f"Composio MCP URL: {COMPOSIO_MCP_URL}")

What's happening:

Authenticates to Composio with your API key
Declares Google ADK as the provider
Spins up a short-lived MCP endpoint for your user and selected toolkit
Stores the MCP HTTP URL for the ADK MCP integration

Set up the McpToolset and create the Agent

python

composio_toolset = McpToolset(
    connection_params=StreamableHTTPConnectionParams(
        url=COMPOSIO_MCP_URL,
        headers={"x-api-key": COMPOSIO_API_KEY}
    )
)

root_agent = Agent(
    model="gemini-2.5-flash",
    name="composio_agent",
    description="An agent that uses Composio tools to perform actions.",
    instruction=(
        "You are a helpful assistant connected to Composio. "
        "You have the following tools available: "
        "COMPOSIO_SEARCH_TOOLS, COMPOSIO_MULTI_EXECUTE_TOOL, "
        "COMPOSIO_MANAGE_CONNECTIONS, COMPOSIO_REMOTE_BASH_TOOL, COMPOSIO_REMOTE_WORKBENCH. "
        "Use these tools to help users with Postmark operations."
    ),
    tools=[composio_toolset],
)

print("\nAgent setup complete. You can now run this agent directly ;)")

What's happening:

Connects the ADK agent to the Composio MCP endpoint through McpToolset
Uses Gemini as the model powering the agent
Lists exact tool names in instruction to reduce misnamed tool calls

Run the agent

bash

# Run in CLI mode
adk run my_agent

# Or run in web UI mode
adk web

Execute the agent from the project root. The web command opens a web portal where you can chat with the agent.

What's happening:

adk run runs the agent in CLI mode
adk web . opens a web UI for interactive testing

Complete Code

Here's the complete code to get you started with Postmark and Google ADK:

python

import os
import warnings

from composio import Composio
from composio_google import GoogleProvider
from dotenv import load_dotenv
from google.adk.agents.llm_agent import Agent
from google.adk.tools.mcp_tool.mcp_session_manager import StreamableHTTPConnectionParams
from google.adk.tools.mcp_tool.mcp_toolset import McpToolset

load_dotenv()
warnings.filterwarnings("ignore", message=".*BaseAuthenticatedTool.*")

GOOGLE_API_KEY = os.getenv("GOOGLE_API_KEY")
COMPOSIO_API_KEY = os.getenv("COMPOSIO_API_KEY")
COMPOSIO_USER_ID = os.getenv("COMPOSIO_USER_ID")

if not GOOGLE_API_KEY:
    raise ValueError("GOOGLE_API_KEY is not set in the environment.")
if not COMPOSIO_API_KEY:
    raise ValueError("COMPOSIO_API_KEY is not set in the environment.")
if not COMPOSIO_USER_ID:
    raise ValueError("COMPOSIO_USER_ID is not set in the environment.")

composio_client = Composio(api_key=COMPOSIO_API_KEY, provider=GoogleProvider())

composio_session = composio_client.create(
    user_id=COMPOSIO_USER_ID,
    toolkits=["postmark"],
)

COMPOSIO_MCP_URL = composio_session.mcp.url


composio_toolset = McpToolset(
    connection_params=StreamableHTTPConnectionParams(
        url=COMPOSIO_MCP_URL,
        headers={"x-api-key": COMPOSIO_API_KEY}
    )
)

root_agent = Agent(
    model="gemini-2.5-flash",
    name="composio_agent",
    description="An agent that uses Composio tools to perform actions.",
    instruction=(
        "You are a helpful assistant connected to Composio. "
        "You have the following tools available: "
        "COMPOSIO_SEARCH_TOOLS, COMPOSIO_MULTI_EXECUTE_TOOL, "
        "COMPOSIO_MANAGE_CONNECTIONS, COMPOSIO_REMOTE_BASH_TOOL, COMPOSIO_REMOTE_WORKBENCH. "
        "Use these tools to help users with Postmark operations."
    ),  
    tools=[composio_toolset],
)

print("\nAgent setup complete. You can now run this agent directly ;)")

Conclusion

You've successfully integrated Postmark with the Google ADK through Composio's MCP Tool Router. Your agent can now interact with Postmark using natural language commands.

Key takeaways:

The Tool Router approach dynamically routes requests to the appropriate Postmark tools
Environment variables keep your credentials secure and separate from code
Clear agent instructions reduce tool calling errors
The ADK web UI provides an interactive interface for testing and development

You can extend this setup by adding more toolkits to the toolkits array in your session configuration.

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

Use Postmark MCP with OpenAI Agents SDK

Claude Agent SDK

Use Postmark MCP with Claude Agent SDK

Claude Code

Use Postmark MCP with Claude Code

Claude Cowork

Use Postmark MCP with Claude Cowork

Codex

Use Postmark MCP with Codex

OpenClaw

Use Postmark MCP with OpenClaw

Hermes

Use Postmark MCP with Hermes

CLI

Use Postmark MCP with CLI

LangChain

Use Postmark MCP with LangChain

Vercel AI SDK

Use Postmark MCP with Vercel AI SDK

Mastra AI

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LlamaIndex

Use Postmark MCP with LlamaIndex

CrewAI

Use Postmark MCP with CrewAI

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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. Google ADK 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.

Start with Postmark.It takes 30 seconds.

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

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Customer stories

Teams ship real agents on Composio

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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 Postmark MCP with Google ADK

Connect Postmark without auth hassles

Introduction

Also integrate Postmark with

TL;DR

What is Google ADK?

What is the Postmark 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 Google and Composio

Install dependencies

Set up ADK project

Set environment variables

Import modules and validate environment

Create Composio client and Tool Router session

Set up the McpToolset and create the Agent

Run the agent

Complete Code

Conclusion

Supported Tools

How to build Postmark MCP Agent with another framework

OpenAI Agents SDK

Claude Agent SDK

Claude Code

Claude Cowork

Codex

OpenClaw

Hermes

CLI

LangChain

Vercel AI SDK

Mastra AI

LlamaIndex

CrewAI

Explore Other Toolkits

Supabase

Codeinterpreter

GitHub

Ably

Frequently asked questions

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

Can I use Tool Router MCP with Google ADK?+

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

How safe is my data with Composio Tool Router?+

Start with Postmark.It takes 30 seconds.

Teams ship real agents on Composio