How to Connect Postmark to an AI Agent
Auth setup
1. In the Postmark dashboard, create a Server (one per environment — prod/staging). 2. Copy the Server API Token from the Server > API Tokens tab. 3. Verify a Sender Signature or Domain before sending. 4. Store tokens in POSTMARK_SERVER_TOKEN env var.
Key facts
| Base URL | https://api.postmarkapp.com/ |
|---|
| API version | v1 (implicit) |
|---|
| Auth | Token authentication via custom headers: `X-Postmark-Server-Token` for transactional operations (bound to a single Postmark Server), or `X-Postmark-Account-Token` for account-level operations (managing servers, domains). NOT Bearer auth. |
|---|
| Scopes | Server tokens: scoped to one Server. Account tokens: full account access. |
|---|
| Request body | application/json |
|---|
| Pagination | Offset-based: `count` and `offset` query params on list endpoints. |
|---|
| Rate limit | No hard per-second rate limit — Postmark is optimized for high throughput. Large accounts can send millions/hour. 429 responses indicate abuse-detection triggers (e.g., unverified senders). |
|---|
| Error format | JSON: {"ErrorCode":300,"Message":"..."} — note PascalCase fields (Postmark uses .NET conventions). |
|---|
Key endpoints
| Method | Path | Description |
|---|
POST | /email | Send a single transactional email |
POST | /email/batch | Send up to 500 emails in one request |
POST | /email/withTemplate | Send using a stored template with merge variables |
GET | /messages/outbound | List sent messages with filtering |
GET | /stats/outbound | Delivery/bounce/open/click statistics |
GET | /bounces | List bounced addresses |
Quickstart
POST https://api.postmarkapp.com/email
X-Postmark-Server-Token: {server_token}
Content-Type: application/json
Accept: application/json
{"From":"hello@yourdomain.com","To":"user@example.com","Subject":"Hi","TextBody":"Hello","MessageStream":"outbound"}
Response: {"To":"user@example.com","SubmittedAt":"...","MessageID":"...","ErrorCode":0,"Message":"OK"}
Agent pitfalls & tips
- Authentication is NOT Bearer — use `X-Postmark-Server-Token` header. Many generic HTTP clients will need custom header config.
- All JSON field names are PascalCase (From, To, TextBody, MessageID) — a Postmark quirk from its .NET roots.
- MessageStream field distinguishes transactional ("outbound") from broadcast ("broadcast") — mixing them violates Postmark TOS.
- Bounces must be handled — Postmark suppresses auto-retried bounced addresses but expects you to clean your list.
- Postmark's strong point is deliverability — SPF/DKIM setup is enforced before sending, which is why inbox placement is high.
- Batch endpoint (up to 500 messages) is the right choice for newsletters — single /email is for 1-to-1 transactional.
Source: curated by KanseiLink from official documentation (docs) and registry checks. Last reviewed: 2026-04-10. Specs change — verify against the official docs before production use.
Frequently Asked Questions
What is Postmark's AEO score?
▼
Postmark has an AEO score of 0.50 and is rated BB (Partial agent connectivity). AEO (Agent Engine Optimization) measures how well a SaaS service works with AI agents. Scores range from 0.00 to 1.00, with grades from AAA (best) to D (not agent-ready).
Is Postmark AI-agent-ready?
▼
Postmark is currently connectable for AI agent use. API access is available but no dedicated MCP server has been published yet. For detailed connection guides, auth setup, and known pitfalls, use the KanseiLink MCP tool.
How does Postmark compare to other Marketing services?
▼
In the Marketing category, Postmark is rated BB. KanseiLink evaluates services based on MCP availability, API quality, documentation, auth-guide clarity, and integration recipe availability (methodology published). Visit the full rankings at kansei-link.com to see how Postmark compares.
How can I integrate Postmark with an AI agent?
▼
The fastest way to integrate Postmark with an AI agent is through KanseiLink MCP. Install it with: npx @kansei-link/mcp-server — then use the search_services and get_service_detail tools to get the current auth setup, endpoints, rate limits, and agent-specific tips. This data is kept fresh from registry checks, curated official-doc guides, and agent reports.
How do I authenticate with Postmark?
▼
Token authentication via custom headers: `X-Postmark-Server-Token` for transactional operations (bound to a single Postmark Server), or `X-Postmark-Account-Token` for account-level operations (managing servers, domains). NOT Bearer auth. Setup: 1. In the Postmark dashboard, create a Server (one per environment — prod/staging). 2. Copy the Server API Token from the Server > API Tokens tab. 3. Verify a Sender Signature or Domain before sending. 4. Store tokens in POSTMARK_SERVER_TOKEN env var.
What are Postmark's API rate limits?
▼
No hard per-second rate limit — Postmark is optimized for high throughput. Large accounts can send millions/hour. 429 responses indicate abuse-detection triggers (e.g., unverified senders).