Send emails with Postmark using Claude and other MCP-compatible AI assistants.
- Exposes a Model Context Protocol (MCP) server backed by your Postmark account
- 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
- 📒 API Documentation
- 🔎 API Explorer
- 📖 Engineering Articles
- 📝 Changelog — what's new in each release
We'd love to hear from you! Please share your feedback and suggestions using our feedback form.
Follow us on X - @postmarkapp
- Node.js v20 or higher
- A Postmark account and server token
Clone the repository:
git clone https://github.com/ActiveCampaign/postmark-mcp
cd postmark-mcpInstall dependencies:
npm install
# or
yarn
# or
bun installCreate your own environment file from the example
cp .env.example .envEdit 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.
| 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) |
| 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:
npm start
# or
yarn start
# or
bun startSmoke 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.
# 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.mjsThe 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.
After installing the MCP, update your configuration to set:
POSTMARK_SERVER_TOKENDEFAULT_SENDER_EMAILDEFAULT_MESSAGE_STREAM(default:outbound)
Install directly from npm without managing a local copy:
{
"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"
}
}
}
}{
"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.
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.
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:
{
"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
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:
{
"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
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 (
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:
{
"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
...
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:
{
"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.
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}}
Retrieves a single template's full content (HTML body, text body, subject, type).
Payload: { "templateIdOrAlias": "welcome" } — accepts numeric ID or string alias.
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:
{
"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".
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).
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" }
Validates template content (Mustachio syntax, undefined variables) without saving. At least one of subject, htmlBody, or textBody is required.
Expected Payload:
{
"subject": "Order #{{order_id}}",
"htmlBody": "<p>Thanks {{name}}</p>",
"textBody": "Thanks {{name}}",
"testRenderModel": { "order_id": 42, "name": "John" },
"templateType": "Standard"
}Searches the outbound message history.
Expected Payload (all filters optional):
{
"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).
Retrieves full details and event timeline for a single outbound message.
Payload: { "messageId": "0a1b2c3d-..." }
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:
{
"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.
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):
{
"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.
Returns the raw SMTP dump for a bounce. Bounce dumps are retained for 30 days.
Payload: { "bounceId": 123456 }
Reactivates a deactivated email address (only bounces where CanActivate: true).
Payload: { "bounceId": 123456 }
Lists suppressions for a message stream.
Expected Payload (all optional):
{
"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.
Suppresses up to 50 email addresses on a message stream.
Payload: { "emailAddresses": ["a@example.com", "b@example.com"], "messageStream": "outbound" }
Removes up to 50 addresses from the suppression list. Note: SpamComplaint suppressions cannot be deleted.
Payload: { "emailAddresses": ["a@example.com"], "messageStream": "outbound" }
Unified stats tool. Default behavior returns a friendly headline summary; pass an optional stat for a focused breakdown.
Expected Payload (all optional):
{
"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%)
Returns the Postmark server's name, color, tracking settings, and webhook URLs.
Payload: {}
Lists configured webhooks. Optional messageStream filter.
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:
{
"url": "https://hooks.yourapp.com/postmark",
"messageStream": "outbound",
"openEnabled": true,
"clickEnabled": true,
"deliveryEnabled": false,
"bounceEnabled": true,
"spamComplaintEnabled": true,
"subscriptionChangeEnabled": false
}Deletes a webhook by ID.
Payload: { "webhookId": 1234567 }
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.
All emails are automatically configured with:
TrackOpens: trueTrackLinks: "HtmlAndText"- Message stream from
DEFAULT_MESSAGE_STREAMenvironment variable
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
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:
{
"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.
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: 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.
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.
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.
To secure your webhook receiver, whitelist Postmark's published sending IPs at the network or firewall level so only Postmark can POST to your endpoint.
Because this MCP server can send email and register webhooks, it is a potential target for prompt injection — 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.
MIT © ActiveCampaign