Koltrix developer docs
Email for your product, sent from your own domain.
Send transactional email through a REST API or SMTP, get delivery events by webhook, and read the replies in a shared team inbox. One API key, one dashboard.
curl https://api.koltrix.com/api/v2/emails \
-H "Authorization: Bearer $KOLTRIX_KEY" \
-H "Content-Type: application/json" \
-H "Idempotency-Key: $(uuidgen)" \
-d '{
"from": "[email protected]",
"to": ["[email protected]"],
"subject": "Your invoice is ready",
"body_html": "<p>Thanks for your order.</p>"
}'const res = await fetch("https://api.koltrix.com/api/v2/emails", {
method: "POST",
headers: {
Authorization: `Bearer ${process.env.KOLTRIX_KEY}`,
"Content-Type": "application/json",
"Idempotency-Key": crypto.randomUUID(),
},
body: JSON.stringify({
from: "[email protected]",
to: ["[email protected]"],
subject: "Your invoice is ready",
body_html: "<p>Thanks for your order.</p>",
}),
});
const { id, status } = await res.json(); // status: "queued"import os, uuid, requests
res = requests.post(
"https://api.koltrix.com/api/v2/emails",
headers={
"Authorization": f"Bearer {os.environ['KOLTRIX_KEY']}",
"Idempotency-Key": str(uuid.uuid4()),
},
json={
"from": "[email protected]",
"to": ["[email protected]"],
"subject": "Your invoice is ready",
"body_html": "<p>Thanks for your order.</p>",
},
)
print(res.json()["status"]) # queuedStart here
Koltrix is email for SaaS teams on your own domain: a transactional email API and SMTP relay for your application, and a team inbox where the replies land and your team answers them. One workspace, one domain setup, one bill.
These docs are for the developer side: sending from your code, hearing back through webhooks, setting up your domain, and connecting AI assistants.
What you can build with
| What it does | |
|---|---|
| REST API | POST /api/v2/emails sends mail from your code, with idempotent retries and a message log you can query. |
| SMTP relay | The same sending pipeline for software that only speaks SMTP. |
| Webhooks | Koltrix calls your server when a message is sent, bounces, is opened or clicked. |
| Replies | Answers to your transactional mail arrive in the team inbox, threaded and counted on the message. |
| Custom domains | Five DNS records and your domain sends and receives through Koltrix, signed with its own DKIM key. |
| AI assistants (MCP) | Let Claude, ChatGPT, Cursor and other assistants search, read, organise and draft mail in your inbox. They never send. |
| Newsletters and sequences | Lists, broadcasts and timed email series, over the API only for now. |
Everything you send shares one suppression list, one signing setup and one message log, so an address that bounced from a broadcast isn't mailed by your receipts either.
A first request
curl https://api.koltrix.com/api/v2/emails \
-H "Authorization: Bearer $KOLTRIX_KEY" \
-H "Content-Type: application/json" \
-H "Idempotency-Key: welcome-user-8812" \
-d '{
"from": "[email protected]",
"to": ["[email protected]"],
"subject": "Welcome to Acme",
"body_html": "<p>Thanks for signing up. Reply to this email if you get stuck.</p>"
}'[email protected] is a real mailbox in your team inbox, so when the new user
replies, a person on your team sees it and can answer.
Find your way
| If you want to… | Read |
|---|---|
| Send your first email | Quickstart |
| Create and scope API keys | Authentication |
| Send from your code, in depth | Sending email |
| Use SMTP credentials instead | SMTP relay |
| Be told about bounces and opens | Webhooks |
| Set up your domain's DNS | Custom domains and DNS |
| Keep your mail out of spam | Deliverability and suppressions |
| Connect Claude or ChatGPT to your inbox | AI assistants (MCP) |
| Look up an endpoint | API reference |
| Understand an error | Errors |
| Check your plan's limits | Limits and quotas |
Things Koltrix doesn't do
- No SMS or push notifications. Email only.
- AI never sends, forwards or deletes mail for you. Koltrix's assistants and the AI assistants connection can read, sort and draft, but every message is sent by a person clicking Send in Koltrix.
- No sending through other providers. Koltrix delivers from its own mail servers.
- No compliance certifications yet. Koltrix is not SOC 2 or HIPAA certified. If you need that, email us before you sign up.
Help
Email [email protected]; we answer within one business day. Common problems and their fixes are in Troubleshooting, and what changed recently is in the Changelog.