# Koltrix

> Koltrix is email for SaaS teams on your own domain: a transactional email REST API (POST /api/v2/emails), an SMTP relay, signed webhooks, a team inbox for replies, and an MCP server so Claude, ChatGPT and Cursor can read, organise and draft mail.

These docs are written for developers and for AI coding assistants. Every page is available as Markdown by adding `.md` to its URL. The whole documentation in one file is https://docs.koltrix.com/llms-full.txt. The API key is read from the environment variable `KOLTRIX_API_KEY`; the REST API is `https://api.koltrix.com/api/v2`; the MCP server is `https://mcp.koltrix.com/mcp`.

## Get started

- [Introduction](https://docs.koltrix.com/index.md): Koltrix developer docs: send transactional email with a REST API or SMTP, get delivery events by webhook, set up your domain, and connect AI assistants.
- [Quickstart](https://docs.koltrix.com/quickstart.md): From a new Koltrix account to your first email sent through the API: add a domain, add an address, create an API key and send.
- [Authentication](https://docs.koltrix.com/authentication.md): API keys for the Koltrix REST API and SMTP relay: creating keys, scopes, which scope each endpoint needs, rotation, and the 401 and 403 errors.

## Send

- [Sending email](https://docs.koltrix.com/sending-email.md): Send transactional email with POST /api/v2/emails: the request fields, the response, idempotent retries, tracking, statuses, and code samples in cURL, Node, Python, Go and PHP.
- [SMTP relay](https://docs.koltrix.com/smtp-relay.md): Send through Koltrix from any SMTP client: host, port 2525, API-key authentication, what the relay reads from your message, limits, reply codes and examples.
- [Domains and DNS](https://docs.koltrix.com/domains.md): The five DNS records Koltrix needs for your domain (ownership, MX, SPF, DKIM, DMARC), what each one does, how to add them at Cloudflare, GoDaddy, Namecheap and Route 53, and how existing domains upgrade.
- [Deliverability](https://docs.koltrix.com/deliverability.md): How Koltrix protects your sending reputation: the suppression list, hard bounces, unsubscribes, DKIM signing, open and click tracking, and pacing for new domains.
- [Newsletters](https://docs.koltrix.com/newsletters.md): Newsletter lists, subscribers and broadcasts over the Koltrix API: creating lists, adding and importing subscribers, unsubscribes, sending a broadcast and merge variables.
- [Sequences](https://docs.koltrix.com/sequences.md): Timed email series over the Koltrix API: create a sequence on a list, add steps with delays, and how enrolment, unsubscribes and suppressions work.

## Receive

- [Replies](https://docs.koltrix.com/replies.md): Replies to the email you send land in your Koltrix team inbox, threaded with the message that caused them, and are counted on the message.
- [Webhooks](https://docs.koltrix.com/webhooks.md): Get an HTTPS POST when Koltrix sends, bounces, or sees an open or click on your mail: event types, payloads, the HMAC-SHA256 signature and how to verify it.

## AI

- [Build with AI](https://docs.koltrix.com/ai.md): Copy-and-paste prompts that let an AI coding assistant integrate Koltrix correctly.
- [Connect an assistant (MCP)](https://docs.koltrix.com/mcp.md): Connect Claude, ChatGPT, Cursor and other AI assistants to your Koltrix inbox with the Model Context Protocol: setup for each app, sign-in and permissions, every tool, and the safety rules.

## Reference

- [API reference](https://docs.koltrix.com/api-reference.md): Every public /api/v2 endpoint with parameters, request examples and responses.
- [Errors](https://docs.koltrix.com/errors.md): Every error the Koltrix REST API returns: the status codes, the JSON bodies, what each one means and whether to retry.
- [Limits and quotas](https://docs.koltrix.com/limits.md): Every limit Koltrix enforces, per plan: sends, storage, domains, addresses, seats and AI actions.

## API endpoints

- [Send an email](https://docs.koltrix.com/api-reference/send-email.md): POST /api/v2/emails
- [List messages](https://docs.koltrix.com/api-reference/list-messages.md): GET /api/v2/messages
- [Get a message](https://docs.koltrix.com/api-reference/get-message.md): GET /api/v2/messages/:id
- [List a message's events](https://docs.koltrix.com/api-reference/get-message-events.md): GET /api/v2/messages/:id/events
- [Get the current key](https://docs.koltrix.com/api-reference/get-me.md): GET /api/v2/me
- [List lists](https://docs.koltrix.com/api-reference/list-lists.md): GET /api/v2/lists
- [Create a list](https://docs.koltrix.com/api-reference/create-list.md): POST /api/v2/lists
- [Get a list](https://docs.koltrix.com/api-reference/get-list.md): GET /api/v2/lists/:id
- [Update a list](https://docs.koltrix.com/api-reference/update-list.md): PATCH /api/v2/lists/:id
- [Delete a list](https://docs.koltrix.com/api-reference/delete-list.md): DELETE /api/v2/lists/:id
- [List subscribers](https://docs.koltrix.com/api-reference/list-subscribers.md): GET /api/v2/lists/:id/subscribers
- [Add a subscriber](https://docs.koltrix.com/api-reference/create-subscriber.md): POST /api/v2/lists/:id/subscribers
- [Import subscribers from CSV](https://docs.koltrix.com/api-reference/import-subscribers.md): POST /api/v2/lists/:id/subscribers/import
- [Delete a subscriber](https://docs.koltrix.com/api-reference/delete-subscriber.md): DELETE /api/v2/lists/:id/subscribers/:sub_id
- [Unsubscribe a subscriber](https://docs.koltrix.com/api-reference/unsubscribe-subscriber.md): POST /api/v2/lists/:id/subscribers/:sub_id/unsubscribe
- [Send a broadcast](https://docs.koltrix.com/api-reference/send-broadcast.md): POST /api/v2/lists/:id/broadcast
- [List sequences](https://docs.koltrix.com/api-reference/list-sequences.md): GET /api/v2/sequences
- [Create a sequence](https://docs.koltrix.com/api-reference/create-sequence.md): POST /api/v2/sequences
- [Delete a sequence](https://docs.koltrix.com/api-reference/delete-sequence.md): DELETE /api/v2/sequences/:id
- [List a sequence's steps](https://docs.koltrix.com/api-reference/list-sequence-steps.md): GET /api/v2/sequences/:id/steps
- [Add a step](https://docs.koltrix.com/api-reference/add-sequence-step.md): POST /api/v2/sequences/:id/steps
- [Delete a step](https://docs.koltrix.com/api-reference/delete-sequence-step.md): DELETE /api/v2/sequences/:id/steps/:step_id

## Optional

- [Troubleshooting](https://docs.koltrix.com/troubleshooting.md): Fixes for the common Koltrix problems: mail not arriving, From address refused, 401, 403 and 429 errors, domains that won't verify, webhooks, the SMTP relay and AI assistants.
- [FAQ](https://docs.koltrix.com/faq.md): Common questions about Koltrix: switching from another provider, pricing, where data lives, AI, API stability, workspaces and deliverability.
- [Integrations](https://docs.koltrix.com/integrations.md): Recipes for wiring Koltrix into other tools: Stripe receipts, GitHub notifications, Slack alerts on bounces, Zapier, Make and n8n, and AI assistants.
- [Changelog](https://docs.koltrix.com/changelog.md): Changes to the Koltrix API, SMTP relay, webhooks, domain setup and these docs, newest first.

- [OpenAPI 3.1 description (YAML)](https://docs.koltrix.com/openapi.yaml): generated from the same endpoint data as the API reference
- [Full documentation in one file](https://docs.koltrix.com/llms-full.txt): every page above, concatenated