Welcome to Koltrix

Koltrix is one hosted email platform instead of five. A transactional API, a real team inbox, full newsletter and drip automation, an SMTP relay, and per-account analytics — wired together behind a single API key, billed on a single invoice.

If you've ever signed up for Mailgun and Postmark and Mailchimp and ConvertKit and a separate "team inbox" SaaS, you already know why this exists. Koltrix gives one team — typically a SaaS founder, an indie operator, or an agency — every email surface they need from a single hosted service.

Get started in 5 minutes — head to the Quickstart to send your first email end-to-end.

Need a key? Create one in the dashboard at app.koltrix.com/api-keys. Keys are shown exactly once, so copy yours somewhere safe.

Who Koltrix is for

• SaaS teams that need transactional sending, a customer support inbox, and product update newsletters without paying three vendors.
• Agencies managing mail for several client accounts through one dashboard, with proper isolation between them.
• Solo founders who want one bill, one dashboard, and a single API to build against.
• Engineers who want a real REST API, real SMTP, real webhooks, and no scattered "deliverability microservices."

The four product surfaces

All four share the same outbound table, the same suppression list, the same DKIM signer, and the same webhook stream — so a bounce on a campaign suppresses that address for transactional too, and your dashboard's "delivery rate" graph is genuinely cross-surface.

How it differs from Mailgun / Postmark / Resend

Those are excellent — at one thing. They send transactional email. To run a real business you also need a place to read replies, a newsletter tool, an embed form for your landing page, and a way to give a customer-success teammate an inbox without giving them production API keys. Today that's five vendors, five bills, five audit logs, and five different ideas about who your customers are.

Koltrix collapses that stack:

• One product: the inbox, the API, and the newsletter UI all live in the same dashboard.
• One identity model: invite teammates and manage roles in one place.
• One pipeline: every send — transactional, SMTP, broadcast, drip — flows through the same worker, same suppression list, same webhooks.
• One bill: Stripe handles the subscription; no per-vendor surprises.

30-second tour

Send a transactional email with curl:

curl https://api.koltrix.com/api/v2/emails \
  -H "Authorization: Bearer kx_..." \
  -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>",
    "body_text": "Thanks for your order."
  }'

Collect a subscriber from your own landing page with no API key in the browser:

<form action="https://api.koltrix.com/api/v1/public/lists/PUBLIC_TOKEN/subscribe"
      method="post">
  <input name="email" type="email" placeholder="[email protected]" required />
  <!-- Honeypot: bots fill it, humans don't. -->
  <input name="_hp" type="text" style="display:none" tabindex="-1" autocomplete="off" />
  <button type="submit">Subscribe</button>
</form>

PUBLIC_TOKEN is the per-list token from Newsletters → list → Embed. Both calls land in the same account, behind the same dashboard you read.

Pick a path

What's deliberately not in this product

To keep the surface honest:

• No SMS or push. Email only.
• No "AI agents that read your inbox and act on it." AI features summarise and draft replies; you still hit Send.
• No multi-vendor SMTP fallback. Koltrix delivers from its own infrastructure — good for deliverability and reputation, no magical rerouting through someone else's network.
• No vendored compliance claims. We are not SOC 2 certified, GDPR certified, or HIPAA certified today. If that's a hard requirement, please reach out before signing up.

How the pieces fit together

The four surfaces above share infrastructure on purpose. A bounce flagged by the transactional API adds the recipient to a global suppression list that newsletter broadcasts honour automatically. A subscriber added through your embedded signup form drops into the same list the dashboard reads from. A drip sequence step is just another outbound message, signed by the same DKIM key, tracked by the same pixel, and delivered to the same webhook endpoint.

That's the architectural bet behind Koltrix: collapsing five almost-the- same SaaS products into one well-factored platform saves an enormous amount of glue code, and gives you a single audit log across every email surface instead of five different ones in five different vendor dashboards.

Need help?

Email [email protected] — we respond within one business day. The full API surface is documented under API reference — every endpoint, every request shape, every error response.