HTTP API · operational

Postmark

Transactional email with fast delivery and per-message tracking.

Send single or batch email, use templates, read delivery, bounce and open events.

endpoint: https://api.postmarkapp.com
auth: X-Postmark-Server-Token header
try it: tested example call
curl -s -X POST https://api.postmarkapp.com/email -H "X-Postmark-Server-Token: $POSTMARK_TOKEN" -H "Content-Type: application/json" -d '{"From":"you@example.com","To":"dest@example.com","Subject":"Hi","TextBody":"Hello"}'
capabilities: send_email · batch_send · templates · delivery_events
tags: email · transactional
pricing: per 1k emails
i/o: application/json → json
docs: https://postmarkapp.com/developer
machine-readable: /api/public/registry/postmark-api

Follow this tool

Get an alert when Postmark goes down, comes back, or quietly changes shape (response schema or tool list). Free for up to 3 tools. Pro: 100 tools + webhooks for your agents.

Get a key in one call

No account, no card

100 calls/day anonymous · 1,000/day with this free key · 50,000/day on Agent Pro. The key is returned instantly in the response — send it as the x-api-key header on any /api/public/* request. The key also lets you follow up to 3 tools and get an alert when one goes down or quietly changes shape. Email is optional; add yours to receive alerts, then confirm them from your inbox.

tested example call

curl -s -X POST https://agentnexus.app/api/public/keys \
  -H 'content-type: application/json' \
  -d '{"agent":"my-agent","purpose":"tool discovery","email":"you@example.com"}'

Use it from your agent

Point any MCP-capable agent (Claude, Cursor, your own) at the no-auth endpoint — it can then find Postmark and every other listed interface on its own:

tested example call

claude mcp add --transport http agent-nexus https://agentnexus.app/api/public/mcp

Agents can discover Postmark through the Agent Nexus MCP server, /llms.txt or the discovery API.