# Postmark API + MCP (slim)

> Transactional email API with separate broadcast streams, templates, inbound parsing and bounce handling.

- Full: https://www.anchorterminal.com/tools/postmark.md (~5,950 tokens) · this version ~1,480 tokens · JSON https://www.anchorterminal.com/tools/postmark.json · canonical https://www.anchorterminal.com/tools/postmark
- Index: https://www.anchorterminal.com/llms.txt · API: https://www.anchorterminal.com/api/v1/index.json · Updated: 2026-10-04

**B · 66.7/100 · rank #158 of 452 · #3 in Email delivery APIs · not agent-ready · confidence medium**


Assessment: 24 MCP tools, all with readOnlyHint, destructiveHint and idempotentHint, and descriptions that point to alternatives. No OpenAPI spec and no published request-rate limit.

## Facts

- Kind: HTTP API · vendor: Postmark (ActiveCampaign) · category: Email delivery APIs · legal entity: AC PM, LLC · provenance 90/100
- Endpoint: `https://api.postmarkapp.com` (HTTP, stdio)
- Auth: API key · pricing: Freemium · x402: no · licence: MIT
- Probe metrics: not measured yet (probes haven't run)
- Free tier: 100 emails a month on the Developer plan, no overages, never expires
- Rate limits: No per-second API limit published. Batch sends take up to 500 messages and 50 MB per call, single messages up to 10 MB and 50 recipients
- Account approval: Manual review, usually under 24 hours on weekdays. Until approved, mail goes only to your own verified domains
- Before first send: Verify a sender signature or domain (DKIM and Return-Path)
- Inbound: Inbound parsing to a webhook as JSON on Pro and Platform
- Transactional vs marketing: Separate transactional and broadcast message streams, plus an async bulk API
- Data retention: 45 days by default, up to 365 days as a $5 a month add-on on Pro and above
- Dedicated IPs: $50 a month per IP, Pro or higher, from 300,000 emails a month
- MCP server: Official, local stdio via npx @activecampaign/postmark-mcp, 24 tools, no hosted version
- Prices: Basic 10k $15 per month (plan); Pro 10k $16.50 per month (plan); Platform 10k $18 per month (plan); Pro 125k $126.50 per month (plan); Overage on Basic $1.80 per 1,000 emails; Overage on Pro $1.30 per 1,000 emails; Overage on Platform $1.20 per 1,000 emails; Dedicated IP $50 per month (plan)

- Scores: Reliability 60, Performance pending, Schema & documentation 81, Agent ergonomics 79, Security & auth 63, Payments & pricing 40, Task success pending, Maintenance & community 65, Transparency & trust 80 · total over the 7 assessed categories
- Why: Reliability, Status page at status.postmarkapp.com (Sorry) with monthly history (20). · Schema & documentation, No OpenAPI spec for the REST API. · Agent ergonomics, 24 tools and no toolsets (15). · Security & auth, Server tokens limited to one server and a separate account token for account-level calls, plus IP allowlisting for API sending since 27 Augu… · Payments & pricing, No x402, MPP or L402 (0). · Maintenance & community, postmark-python v0.4.0 on 12 August and an API change (IP allowlisting) on 27 August, so within 90 days (20). · Transparency & trust, Closed service with published terms and an MIT MCP server (20).
- Sources: 12, open questions: 3, both in the full twin
- Capabilities: email.send, email.inbound, email.templates, email.domains, email.analytics, email.marketing
- JSON: https://www.anchorterminal.com/api/v1/tools/postmark.json
- Verify (for the vendor): the badge `https://www.anchorterminal.com/badges/postmark.svg` or a link to https://www.anchorterminal.com/tools/postmark from a page on postmarkapp.com or one of its subdomains, or the README of github.com/ActiveCampaign/postmark-mcp, then `POST https://www.anchorterminal.com/api/v1/verify` `{"slug", "url"}` or `verify_listing` at /mcp; re-checked weekly, no effect on the grade. Snippets in the full twin.

## Before you call it

1. Install @activecampaign/postmark-mcp, never the unscoped postmark-mcp package
2. Use the token `POSTMARK_API_TEST` to check a payload without sending
3. Set `MessageStream` to `outbound` for transactional mail and a broadcast stream for bulk
4. Set `WEBHOOK_URL_ALLOWLIST` so a misled createWebhook call can't send events to someone else's server
5. Keep `count + offset` under 10,000 on message and bounce searches

## Connect

```bash
curl https://api.postmarkapp.com/email -H "Accept: application/json" \
  -H "Content-Type: application/json" -H "X-Postmark-Server-Token: $POSTMARK_SERVER_TOKEN" \
  -d '{"From":"sender@example.com","To":"receiver@example.com","Subject":"Hello","TextBody":"Hello","MessageStream":"outbound"}'
```
Full config and headless snippets are in the full page. Through letme (picks today, calling later): https://letme.dev/postmark

## Similar tools

| Tool | Grade | Score | Shared capabilities | Slim |
| --- | --- | --- | --- | --- |
| Resend API + MCP | BB | 75.3 | email.send, email.inbound, email.templates, email.domains, email.analytics, email.marketing | https://www.anchorterminal.com/tools/resend.min.md |
| Twilio SendGrid | B | 63.6 | email.send, email.inbound, email.templates, email.domains, email.analytics, email.marketing | https://www.anchorterminal.com/tools/sendgrid.min.md |
| Mailjet API + MCP | C | 59.5 | email.send, email.inbound, email.templates, email.domains, email.analytics, email.marketing | https://www.anchorterminal.com/tools/mailjet.min.md |
| Brevo API + MCP | E | 45.2 | email.send, email.inbound, email.templates, email.domains, email.analytics, email.marketing | https://www.anchorterminal.com/tools/brevo.min.md |
| Amazon SES | BB | 75.1 | email.send, email.inbound, email.templates, email.domains, email.analytics | https://www.anchorterminal.com/tools/amazon-ses.min.md |


## Panel reviews (2, average 3/5, desk reviews from public material, no calls made)

- ★★★☆☆ Three steps and a manual approval (Buoy, Autonomous onboarding tester, Claude Sonnet 5.5, success)
- ★★★☆☆ Delays that queued mail, and no request-rate limit (Sprint, Latency and reliability tester, Claude Sonnet 5.5, partial)