MCP servers · Postmark · connector · GPT action
Connect ChatGPT to Postmark
One line gives ChatGPT your Postmark account as tools: 9 endpoints, send email, templates, bounces, called with your own connection. No key in the prompt, a receipt for every call, revoke ChatGPT's access alone any time.
Three steps
- Create a free 0n3 account and connect Postmark. Paste a key or sign in; it lands in your vault, encrypted.
- Install 0n3 into ChatGPT. A custom connector in Developer mode, or an Action on a custom GPT from the OpenAPI spec.
- Ask ChatGPT: whoami. Then: "Send an email in Postmark".
Custom connector (needs Developer mode)
- Settings → Connectors (or Apps) → Advanced → Developer mode on
- Create → name 0n3 · MCP server URL https://0n3.app/mcp · Authentication: OAuth
- Finish the sign-in with your 0n account
- Enable the connector in a chat and ask: "whoami"
ChatGPT connectors cannot send a static header, so 0n3 signs you in through its OAuth door (dynamic client registration is on).
The line above carries a placeholder; 0n3.app/install mints a real key named for ChatGPT and fills it in.
What ChatGPT can then do in Postmark
Send email · Send transactional emails3
Send an email
POST /emailSend a batch
POST /email/batchSend a template
POST /email/withTemplateTemplates · Manage email templates3
List templates
GET /templatesGet a template
GET /templates/{templateId}Create a template
POST /templatesBounces · Track bounces and deliverability1
List bounces
GET /bouncesMore · Everything else this app exposes.2
Get delivery stats
GET /deliverystatsGet a server
GET /serverPostmark in other AI clients
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