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Official Postmark MCP server by ActiveCampaign — 24 tools to send, template, search, and diagnose transactional email from Claude, Cursor & other AI assistants.

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# Official Postmark MCP Server&nbsp;&nbsp;&nbsp;[![NPM Version](https://img.shields.io/npm/v/@activecampaign/postmark-mcp.svg)](https://www.npmjs.com/package/@activecampaign/postmark-mcp)&nbsp;&nbsp;![MIT licensed](https://img.shields.io/npm/l/%40activecampaign%2Fpostmark-mcp)

Send emails with Postmark using Claude and other MCP-compatible AI assistants.

## Features
- Exposes a Model Context Protocol (MCP) server backed by your [Postmark account](https://account.postmarkapp.com/sign_up)
- 24 tools spanning email sending (single + batch), templates (CRUD + validation), message search, delivery diagnostics, bounces, suppressions, stats, server info, and webhooks
- MCP tool annotations (`readOnlyHint`, `destructiveHint`) let supporting clients auto-approve safe reads and require confirmation before mutating or destructive operations
- Simple configuration via environment variables
- Comprehensive error handling and graceful shutdown
- Structured JSON logging to stderr with optional log-file persistence; email addresses are partially masked by default
- HTTPS enforcement and optional domain allowlist for webhook registration
- Automatic open/click tracking on every send

## Useful Docs
- [📒 API Documentation](https://postmarkapp.com/developer)
- [🔎 API Explorer](https://postmarkapp.com/api-explorer)
- [📖 Engineering Articles](https://postmarkapp.com/blog/topics/engineering)
- [📝 Changelog](CHANGELOG.md) — what's new in each release

## Feedback
We'd love to hear from you! Please share your feedback and suggestions using our [feedback form](https://forms.gle/zVdZLAJPM81Vo2Wh8).

---

# Setup

## Requirements
- Node.js v20 or higher
- A [Postmark account](https://account.postmarkapp.com/sign_up) and server token

## Installation (Local Development)
**Clone the repository:**
```sh
git clone https://github.com/ActiveCampaign/postmark-mcp
cd postmark-mcp
```

**Install dependencies:**
```sh
npm install
# or
yarn
# or
bun install
```

## Configuration (Local Development)

Create your own environment file from the example

```sh
cp .env.example .env
```

Edit your `.env` to contain your Postmark credentials and settings.

**Important:** This is intended for local development purposes only. Secrets should never be stored in version control and `.env` type files should be added to `.gitignore`.

### Required

| Variable | Description |
|---|---|
| `POSTMARK_SERVER_TOKEN` | Your Postmark server API token |
| `DEFAULT_SENDER_EMAIL` | Default sender email address (must be a verified sender in Postmark) |
| `DEFAULT_MESSAGE_STREAM` | Postmark message stream (e.g., `outbound`) |

### Optional

| Variable | Default | Description |
|---|---|---|
| `AGENT_LABEL` | — | A label for this instance (e.g., `prod`, `staging`). Sent as `X-Agent-Label` on every Postmark API request, useful for identifying traffic sources in logs or support tickets. |
| `WEBHOOK_URL_ALLOWLIST` | — | Comma-separated list of HTTPS URL prefixes that `createWebhook` will accept (e.g., `https://hooks.yourapp.com,https://inbound.corp.io`). When unset, any valid HTTPS URL is accepted. |
| `LOG_FILE` | — | Path to a file where structured JSON logs are appended in addition to stderr. The file is created if it does not exist. No rotation or size cap is applied — use an external tool such as `logrotate` to manage the file in long-running deployments. |
| `LOG_EMAIL_FULL` | `false` | Set to `true` to log email addresses without masking. By default the mailbox portion is partially masked in logs (`u**r@example.com`). |

**Run the server:**

```sh
npm start
# or
yarn start
# or
bun start
```

**Smoke test (requires valid `.env`):**

The repo ships two smoke-test example files. Copy each to its non-example name (which is gitignored) before running, so your local edits — including any verified-sender addresses — never end up committed.

```sh
# Read-only suite (25 checks). Optionally edit RECIPIENT_WITH_HISTORY.
cp smoke-test.example.mjs smoke-test.mjs
npm run smoke

# Mutating suite (full lifecycles + real email sends).
# REQUIRED: edit SENDER and RECIPIENT to two of your verified addresses.
cp smoke-test-mutating.example.mjs smoke-test-mutating.mjs
node smoke-test-mutating.mjs
```

The read-only suite spawns the server over stdio and exercises every read tool against your Postmark account, plus the validation paths for `editTemplate` and `createWebhook`. Does not send mail or mutate state.

The mutating suite runs full create→edit→delete lifecycles for templates (including layout binding), webhooks, and suppressions, and sends real emails between the two addresses you configure. It cleans up after itself. The script refuses to run while the placeholder values are still in place.

## Cursor Quick Install
<div>
  <a href="cursor://anysphere.cursor-deeplink/mcp/install?name=Postmark&config=eyJjb21tYW5kIjoibm9kZSIsImFyZ3MiOlsiaW5kZXguanMiXSwiZW52Ijp7IlBPU1RNQVJLX1NFUlZFUl9UT0tFTiI6IiIsIkRFRkFVTFRfU0VOREVSX0VNQUlMIjoiIiwiREVGQVVMVF9NRVNTQUdFX1NUUkVBTSI6Im91dGJvdW5kIn19">
    <img src="https://img.shields.io/badge/Add_Postmark_MCP_Server-to_Cursor-00A4DB?style=for-the-badge&logo=cursor&logoColor=white" alt="Add Postmark MCP Server to Cursor" />
  </a>
</div>
<br />

After installing the MCP, update your configuration to set:
- `POSTMARK_SERVER_TOKEN`
- `DEFAULT_SENDER_EMAIL`
- `DEFAULT_MESSAGE_STREAM` (default: `outbound`)

## MCP Client Configuration

### Using npx (recommended — no clone required)

Install directly from npm without managing a local copy:

```json
{
  "mcpServers": {
    "postmark": {
      "command": "npx",
      "args": ["-y", "@activecampaign/postmark-mcp"],
      "env": {
        "POSTMARK_SERVER_TOKEN": "your-postmark-server-token",
        "DEFAULT_SENDER_EMAIL": "your-sender-email@example.com",
        "DEFAULT_MESSAGE_STREAM": "outbound"
      }
    }
  }
}
```

### Using a local clone

```json
{
  "mcpServers": {
    "postmark": {
      "command": "node",
      "args": ["/absolute/path/to/postmark-mcp/index.js"],
      "env": {
        "POSTMARK_SERVER_TOKEN": "your-postmark-server-token",
        "DEFAULT_SENDER_EMAIL": "your-sender-email@example.com",
        "DEFAULT_MESSAGE_STREAM": "outbound"
      }
    }
  }
}
```

Both snippets work with **Claude Desktop** (`~/Library/Application Support/Claude/claude_desktop_config.json`), **Cursor** (`.cursor/mcp.json`), and any other MCP client that accepts the standard JSON configuration format.

## Tools
This section provides a complete reference for the Postmark MCP server tools including example prompts and payloads. The server registers **24 tools** organized into eight categories.

### Table of Contents
- [Email](#email)
  - [sendEmail](#sendemail)
  - [sendEmailWithTemplate](#sendemailwithtemplate)
  - [sendBatch](#sendbatch)
  - [sendBatchWithTemplate](#sendbatchwithtemplate)
- [Templates](#templates)
  - [listTemplates](#listtemplates)
  - [getTemplate](#gettemplate)
  - [createTemplate](#createtemplate)
  - [editTemplate](#edittemplate)
  - [deleteTemplate](#deletetemplate)
  - [validateTemplate](#validatetemplate)
- [Messages](#messages)
  - [searchOutboundMessages](#searchoutboundmessages)
  - [getMessageDetails](#getmessagedetails)
- [Diagnostics](#diagnostics)
  - [diagnoseDelivery](#diagnosedelivery)
- [Bounces](#bounces)
  - [searchBounces](#searchbounces)
  - [getBounceDump](#getbouncedump)
  - [activateBounce](#activatebounce)
- [Suppressions](#suppressions)
  - [listSuppressions](#listsuppressions)
  - [createSuppressions](#createsuppressions)
  - [deleteSuppressions](#deletesuppressions)
- [Stats & Server](#stats--server)
  - [getDeliveryStats](#getdeliverystats)
  - [getServerInfo](#getserverinfo)
- [Webhooks](#webhooks)
  - [listWebhooks](#listwebhooks)
  - [createWebhook](#createwebhook)
  - [deleteWebhook](#deletewebhook)

---

## Email

### sendEmail
Sends a transactional email to one recipient or up to 50 recipients.

**Example Prompt:**
```
Send an email using Postmark to recipient@example.com with the subject "Meeting Reminder" and the message "Don't forget our team meeting tomorrow at 2 PM."
```

**Expected Payload:**
```json
{
  "to": "recipient@example.com",
  "subject": "Meeting Reminder",
  "textBody": "Don't forget our team meeting tomorrow at 2 PM.",
  "htmlBody": "<p>Don't forget our team meeting tomorrow at 2 PM.</p>",
  "from": "sender@example.com",
  "cc": "manager@example.com",
  "bcc": "archive@example.com",
  "replyTo": "support@example.com",
  "tag": "meetings"
}
```

`to` accepts a single address or an array of up to 50 addresses. `htmlBody`, `from`, `cc`, `bcc`, `replyTo`, and `tag` are optional. If `from` is omitted, `DEFAULT_SENDER_EMAIL` is used.

**Response:**
```
Email sent successfully!
MessageID: 0a1b2c3d-...
To: recipient@example.com
Subject: Meeting Reminder
```

### sendEmailWithTemplate
Sends an email using a Postmark template.

**Example Prompt:**
```
Send the "welcome" template to customer@example.com with name "John Doe" and login_url "https://myapp.com/login".
```

**Expected Payload:**
```json
{
  "to": "customer@example.com",
  "templateAlias": "welcome",
  "templateModel": {
    "name": "John Doe",
    "login_url": "https://myapp.com/login"
  },
  "from": "sender@example.com",
  "tag": "onboarding"
}
```

Provide **either** `templateId` (number) **or** `templateAlias` (string), not both.

**Response:**
```
Template email sent successfully!
MessageID: 0a1b2c3d-...
To: customer@example.com
Template: welcome
```

### sendBatch
Sends up to 500 emails in a single API call. Each message is fully independent — its own recipient, subject, and body. This wraps Postmark's *synchronous* batch endpoint (`POST /email/batch`), which returns immediate per-message results.

> **Note:** Postmark also offers an asynchronous [bulk email API](https://postmarkapp.com/developer/api/bulk-email) (`POST /email/bulk`) for large-volume jobs with no message-count cap and a 50 MB payload limit. That endpoint uses a submit-and-poll workflow and is not currently wrapped by this MCP server.

**Expected Payload:**
```json
{
  "messages": [
    {
      "to": "alice@example.com",
      "subject": "Order #1234 confirmed",
      "textBody": "Thanks Alice — your order is on its way.",
      "tag": "order-confirmation"
    },
    {
      "to": "bob@example.com",
      "subject": "Order #1235 confirmed",
      "textBody": "Thanks Bob — your order is on its way.",
      "tag": "order-confirmation"
    }
  ]
}
```

Per-message fields: `to`, `subject`, `textBody` are required. `htmlBody`, `from`, `cc`, `bcc`, `replyTo`, and `tag` are optional. If `from` is omitted on a message, `DEFAULT_SENDER_EMAIL` is used.

**Response:**
```
Sent 2/2 successfully

Successes:
  - alice@example.com — abc-123-def
  - bob@example.com — abc-456-ghi
```

When some messages fail at submission (e.g., suppressed recipients), failures are listed first with their `ErrorCode` and reason:
```
Sent 8/10 successfully (2 failed)

Failures:
  - blocked@example.com — 406: Address has been suppressed.
  - bad@example.com — 300: Inactive recipient
...
```

### sendBatchWithTemplate
Sends up to 500 templated emails — same template, per-recipient template models. Ideal for "render this onboarding template for each new user" flows.

**Expected Payload:**
```json
{
  "templateAlias": "welcome",
  "from": "hello@yourapp.com",
  "tag": "onboarding",
  "recipients": [
    { "to": "alice@example.com", "templateModel": { "name": "Alice", "plan": "Pro" } },
    { "to": "bob@example.com", "templateModel": { "name": "Bob", "plan": "Free" } }
  ]
}
```

Provide **either** `templateId` (number) **or** `templateAlias` (string). Top-level `from` and `tag` apply to all recipients but can be overridden per-recipient. Each recipient also accepts optional `cc`, `bcc`, and `replyTo`.

**Response:** same format as `sendBatch`.

---

## Templates

### listTemplates
Lists saved templates on this server. Returns the first 100 templates; if a server has more than 100, pagination is not yet supported and the response will indicate that results are truncated.

**Response:**
```
Found 2 templates:

• **Welcome**
  - ID: 12345678
  - Alias: welcome
  - Subject: Welcome to {{product_name}}
```

### getTemplate
Retrieves a single template's full content (HTML body, text body, subject, type).

**Payload:** `{ "templateIdOrAlias": "welcome" }` — accepts numeric ID or string alias.

### createTemplate
Creates a new template. Requires `name`. At least one of `htmlBody` or `textBody` must be provided.

`subject` is required for Standard templates and must be **omitted** for Layout templates — Postmark rejects the field on Layouts.

`layoutTemplate` (Standard only) binds the new template to an existing Layout by alias. Without it, the new template renders unwrapped (no chrome from any layout).

**Expected Payload:**
```json
{
  "name": "Order Confirmation",
  "subject": "Your order #{{order_id}} is confirmed",
  "htmlBody": "<h1>Thanks {{name}}</h1>",
  "textBody": "Thanks {{name}}",
  "alias": "order-confirmation",
  "templateType": "Standard",
  "layoutTemplate": "basic"
}
```

`templateType` may be `"Standard"` (default) or `"Layout"`.

### editTemplate
Updates an existing template. Requires `templateIdOrAlias` plus **at least one** updated field (`name`, `subject`, `htmlBody`, `textBody`, `alias`, or `layoutTemplate`).

Pass `"layoutTemplate": null` to unbind a template from its current Layout (the MCP translates this to the empty-string the Postmark API requires for clearing the association).

### deleteTemplate
Permanently deletes a template by ID or alias. Layout templates cannot be deleted while Standard templates are still bound to them — unbind via `editTemplate` first.

**Payload:** `{ "templateIdOrAlias": "order-confirmation" }`

### validateTemplate
Validates template content (Mustachio syntax, undefined variables) without saving. At least one of `subject`, `htmlBody`, or `textBody` is required.

**Expected Payload:**
```json
{
  "subject": "Order #{{order_id}}",
  "htmlBody": "<p>Thanks {{name}}</p>",
  "textBody": "Thanks {{name}}",
  "testRenderModel": { "order_id": 42, "name": "John" },
  "templateType": "Standard"
}
```

---

## Messages

### searchOutboundMessages
Searches the outbound message history.

**Expected Payload (all filters optional):**
```json
{
  "recipient": "user@example.com",
  "fromEmail": "sender@example.com",
  "tag": "marketing",
  "subject": "Welcome",
  "status": "sent",
  "messageStream": "outbound",
  "fromDate": "2025-05-01",
  "toDate": "2025-05-15",
  "count": 50,
  "offset": 0
}
```

`status` is one of `queued`, `sent`, `processed`. `count` is 1–500 (default 50).

### getMessageDetails
Retrieves full details and event timeline for a single outbound message.

**Payload:** `{ "messageId": "0a1b2c3d-..." }`

---

## Diagnostics

### diagnoseDelivery
Composite triage tool. Answers "did my email reach X, and if not, why?" by running message search, suppression check, and bounce history lookups in parallel against a recipient address, then synthesizing a plain-English recommendation.

This is a **diagnostic** tool: it composes multiple Postmark API calls into a single coherent answer rather than mirroring a single endpoint.

**Example Prompt:**
```
Did my email to recipient@example.com get delivered? If not, what should I do?
```

**Expected Payload:**
```json
{
  "recipient": "recipient@example.com",
  "messageId": "0a1b2c3d-...",
  "fromDate": "2026-04-21",
  "toDate": "2026-04-28",
  "messageStream": "outbound"
}
```

All fields except `recipient` are optional. If `messageId` is omitted, the most recent message to the recipient is used. The default search window is the last 7 days.

**Sample response:**
```
Delivery Diagnosis: recipient@example.com
────────────────────────────────────────────────

Suppression: not suppressed on stream "outbound"

Most recent message:
  MessageID: fadeae4e-fb04-4102-9303-9876078c7b81
  Subject:   Welcome to MyApp
  Sent:      2026-04-27T18:42:19.0000000-04:00
  Status:    Sent
  Events:    Delivered, Opened×2, Clicked

Bounce history: none

Recommended action:
  Email was delivered. If recipient says they didn't see it, check their
  spam folder or ask them to whitelist the sender domain.
```

When the recipient is suppressed, the recommendation differs based on reason: `SpamComplaint` is permanent, `HardBounce` may be reactivatable, `ManualSuppression` can be deleted via `deleteSuppressions`.

---

## Bounces

### searchBounces
Searches the bounce log with optional filters by type, recipient, tag, message ID, message stream, date range, and active/inactive status.

**Expected Payload (all optional):**
```json
{
  "type": "HardBounce",
  "inactive": true,
  "emailFilter": "@example.com",
  "tag": "marketing",
  "messageID": "0a1b2c3d-...",
  "messageStream": "outbound",
  "fromDate": "2025-05-01",
  "toDate": "2025-05-15",
  "count": 50,
  "offset": 0
}
```

Supported `type` values (matches Postmark's `BounceType` enum — 22 values): `AddressChange`, `AutoResponder`, `BadEmailAddress`, `Blocked`, `ChallengeVerification`, `DMARCPolicy`, `DnsError`, `HardBounce`, `InboundError`, `ManuallyDeactivated`, `OpenRelayTest`, `SMTPApiError`, `SoftBounce`, `SpamComplaint`, `SpamNotification`, `Subscribe`, `TemplateRenderingFailed`, `Transient`, `Unconfirmed`, `Unknown`, `Unsubscribe`, `VirusNotification`.

### getBounceDump
Returns the raw SMTP dump for a bounce. Bounce dumps are retained for 30 days.

**Payload:** `{ "bounceId": 123456 }`

### activateBounce
Reactivates a deactivated email address (only bounces where `CanActivate: true`).

**Payload:** `{ "bounceId": 123456 }`

---

## Suppressions

### listSuppressions
Lists suppressions for a message stream.

**Expected Payload (all optional):**
```json
{
  "messageStream": "outbound",
  "suppressionReason": "HardBounce",
  "origin": "Recipient",
  "emailAddress": "user@example.com",
  "fromDate": "2025-05-01",
  "toDate": "2025-05-15"
}
```

`suppressionReason` ∈ `HardBounce`, `SpamComplaint`, `ManualSuppression`. `origin` ∈ `Recipient`, `Customer`, `Admin`. If `messageStream` is omitted, `DEFAULT_MESSAGE_STREAM` is used.

### createSuppressions
Suppresses up to 50 email addresses on a message stream.

**Payload:** `{ "emailAddresses": ["a@example.com", "b@example.com"], "messageStream": "outbound" }`

### deleteSuppressions
Removes up to 50 addresses from the suppression list. Note: `SpamComplaint` suppressions cannot be deleted.

**Payload:** `{ "emailAddresses": ["a@example.com"], "messageStream": "outbound" }`

---

## Stats & Server

### getDeliveryStats
Unified stats tool. Default behavior returns a friendly headline summary; pass an optional `stat` for a focused breakdown.

**Expected Payload (all optional):**
```json
{
  "stat": "summary",
  "tag": "marketing",
  "fromDate": "2025-05-01",
  "toDate": "2025-05-15",
  "messageStream": "outbound"
}
```

Supported `stat` values:

| `stat` | What it returns |
|---|---|
| `summary` *(default)* | Headline open / click / bounce / spam rates |
| `overview` | All overview counts (sent, tracked, opens, clicks, bounces, …) |
| `sent` | Sent count |
| `bounces` | Bounce breakdown by type |
| `spam` | Spam complaint count |
| `tracked` | Tracked email count |
| `opens` | Total + unique opens |
| `openPlatforms` | Open platform breakdown (Desktop / Mobile / WebMail / Unknown) |
| `openClients` | Top 10 email clients (Apple Mail, Gmail, …) |
| `openReadTimes` | Read-time histogram |
| `clicks` | Total + unique link clicks |
| `clickBrowsers` | Top 10 browsers used to click |
| `clickPlatforms` | Click platform breakdown (Desktop / Mobile / WebMail / Unknown) |
| `clickLocation` | HTML vs. plain-text click location |

**Default summary response:**
```
Email Delivery Summary

Sent:        74
Tracked:     33  (44.6% of sent)
Open rate:   93.9%  (31/33 unique opens)
Click rate:  4.8%  (10/207 unique links clicked)
Bounced:     1  (1.4%)
Spam:        0  (0.0%)

Period: 2025-05-01 → 2025-05-15
Tag: marketing
```

**Sample `stat: "openPlatforms"` response:**
```
Open Platform Usage

Desktop        20  (64.5%)
  Mobile          0  (0.0%)
  WebMail        11  (35.5%)
  Unknown         0  (0.0%)
```

### getServerInfo
Returns the Postmark server's name, color, tracking settings, and webhook URLs.

**Payload:** `{}`

---

## Webhooks

### listWebhooks
Lists configured webhooks. Optional `messageStream` filter.

### createWebhook
Creates a webhook subscription. Requires a `url` and **at least one** trigger.

**Security note:** Webhooks are persistent — once registered, Postmark will POST event data (opens, clicks, bounces, spam complaints, etc.) to the target URL for all future matching events on that server, until the webhook is deleted. Only register webhooks pointing to URLs you control. Use `WEBHOOK_URL_ALLOWLIST` to restrict accepted URLs to known prefixes.

The `url` must use **HTTPS**. HTTP URLs are rejected. If `WEBHOOK_URL_ALLOWLIST` is set, the URL must also match one of the configured prefixes.

**Expected Payload:**
```json
{
  "url": "https://hooks.yourapp.com/postmark",
  "messageStream": "outbound",
  "openEnabled": true,
  "clickEnabled": true,
  "deliveryEnabled": false,
  "bounceEnabled": true,
  "spamComplaintEnabled": true,
  "subscriptionChangeEnabled": false
}
```

### deleteWebhook
Deletes a webhook by ID.

**Payload:** `{ "webhookId": 1234567 }`

## Implementation Details
### API Request Headers
All requests to the Postmark API include the following headers for client identification:

| Header | Description |
|---|---|
| `X-Postmark-Client` | Always `postmark-mcp` — identifies this server as the request origin |
| `X-Postmark-Client-Version` | Version of this MCP server, matching the package version |
| `X-Postmark-MCP-Client` | Name and version of the MCP host application (e.g., `claude-desktop/1.0`), captured from the MCP `initialize` handshake. Omitted if the client does not provide this information. |
| `X-Agent-Label` | Value of the `AGENT_LABEL` environment variable. Omitted when not set. |

This server uses its own HTTP client (no postmark npm package) so that MCP traffic is identifiable as `postmark-mcp` in Postmark logs and support tickets.

### Automatic Configuration
All emails are automatically configured with:
- `TrackOpens: true`
- `TrackLinks: "HtmlAndText"`
- Message stream from `DEFAULT_MESSAGE_STREAM` environment variable

### Error Handling
The server implements comprehensive error handling:
- Validation of all required environment variables
- Graceful shutdown on SIGTERM and SIGINT
- Proper error handling for API calls
- No exposure of sensitive information in logs
- Consistent error message formatting

### Logging
Every tool invocation emits a structured JSON line to **stderr**. If `LOG_FILE` is set, the same line is also appended to that file.

**Log entry shape:**
```json
{
  "timestamp": "2026-06-16T20:34:01.123Z",
  "tool": "sendEmail",
  "clientName": "claude-desktop",
  "clientVersion": "1.0",
  "args": {
    "to": "u**r@example.com",
    "subject": "Meeting Reminder",
    "textBody": "[312ch]"
  },
  "status": "ok",
  "durationMs": 243
}
```

On error, `status` is `"error"` and an `error` field contains the message.

**What is and isn't logged:**

| Data | Logged as |
|---|---|
| Email addresses | Partially masked: `u**r@example.com` (set `LOG_EMAIL_FULL=true` to disable) |
| `htmlBody` / `textBody` | Byte count only: `[312ch]` |
| `templateModel` and other data objects | Key names only: `{ "_keys": ["name", "plan"] }` |
| Batch `messages` / `recipients` arrays | Count + recipient list: `{ "_count": 2, "_recipients": ["u**r@…", "a*b@…"] }` |
| Fields matching `password`, `secret`, `token`, `apikey` | `[redacted]` |
| Tool name, duration, MCP client identity, status | Logged in full |

> Unstructured operational messages (startup, shutdown, API connectivity) continue to write to stderr as plain text alongside the JSON tool logs.

---

## Security Considerations

### Access scope
This MCP server acts with the full permissions of the configured `POSTMARK_SERVER_TOKEN`. It exposes 24 tools — including bulk email sends, template management, webhook registration, and suppression list edits — to any MCP client that connects.

Postmark has [two token types](https://postmarkapp.com/developer/api/overview#authentication): a **Server Token** (used here) and an **Account Token**. Neither supports sub-scoped permissions — a Server Token grants full access to all operations on the server it belongs to. The practical way to limit exposure is structural:

- Create a **dedicated Postmark server** used exclusively for MCP traffic. A compromise is then limited to that server's data and settings rather than your entire account.
- Configure that server with only the message streams and verified sender signatures it actually needs.
- Rotate the token if it is ever exposed.

### Tool blast radius
The 24 tools include several high-impact operations. Below is the breakdown by risk level:

| Category | Tools |
|---|---|
| **Destructive** (irreversible) | `editTemplate`, `deleteTemplate`, `deleteWebhook`, `deleteSuppressions` |
| **Sending** (outbound email) | `sendEmail`, `sendEmailWithTemplate`, `sendBatch`, `sendBatchWithTemplate` |
| **Additive** (account-state changes) | `createTemplate`, `createSuppressions`, `createWebhook`, `activateBounce` |
| **Read-only** | All remaining 12 tools |

All tools carry MCP annotations (`readOnlyHint`, `destructiveHint`, `idempotentHint`). MCP clients that respect annotations — including Cursor and Claude Desktop — can auto-approve safe read-only lookups (`readOnlyHint: true`) and will surface confirmation prompts for anything that isn't a read: sends, template edits, suppression changes, and webhook management. Tools that permanently delete data additionally carry `destructiveHint: true` for clients that distinguish destructive from merely mutating actions.

### Webhook URL policy
`createWebhook` enforces HTTPS on all URLs. Once a webhook is registered, Postmark will POST event data (opens, clicks, bounces, spam complaints) to that URL on an ongoing basis until the webhook is deleted. To prevent a compromised or misdirected tool call from registering a callback you don't control, set `WEBHOOK_URL_ALLOWLIST` to the HTTPS prefixes you own. Audit registered webhooks regularly with `listWebhooks` or via the [Postmark dashboard](https://account.postmarkapp.com).

To secure your webhook receiver, whitelist [Postmark's published sending IPs](https://postmarkapp.com/support/article/800-what-are-the-postmark-ip-addresses) at the network or firewall level so only Postmark can POST to your endpoint.

### Prompt injection risk
Because this MCP server can send email and register webhooks, it is a potential target for [prompt injection](https://owasp.org/www-project-top-10-for-large-language-model-applications/) — where malicious content in an email, template, or repository tricks the AI into invoking a tool with unintended arguments. The mitigations above (dedicated token, tool approval in your MCP client, `WEBHOOK_URL_ALLOWLIST`) reduce the blast radius if this occurs. Never configure auto-approval for sending or destructive tools in untrusted environments.

---

*For more information about the Postmark API, visit [Postmark's Developer Documentation](https://postmarkapp.com/developer).*

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