A transactional API, a real inbox, newsletters, and analytics — together in a single product. One auth, one bill, one source of truth for every message your business sends or receives.
Just finished the migration audit — all DNS records validated, SSL chains intact. I ran the replay suite for 4 hours and saw zero inconsistencies.
Ready to flip production Friday morning. Suggest 9am PT — traffic is at its lowest and SRE is on standby.
Send, receive, broadcast, and measure — under one auth, one dashboard, one bill.
Receive, reply, search, and label across every domain you've verified. Each tenant lives in its own Postgres schema — switching between them is one click, with zero data crossover.
Per-key permissions, idempotency, automatic retries on the same wire your client already speaks.
Lists, segments, drip sequences, A/B subjects, double opt-in, one-click unsubscribe.
Automatic domain warm-up, DKIM via Rspamd, hard-bounce auto-suppression.
HMAC-SHA256 for sent · delivered · bounced · opened · clicked · unsubscribed. Replayable from the UI.
Add as many verified domains as you need. Each gets its own DKIM, MX, and inbox view.
Every entry and exit point is a well-known wire format — no proprietary SDK to learn, no migration headache later.
OpenAPI-described JSON over HTTPS. SDKs for any language with HTTP.
Point your existing mail library at smtp.koltrix.com:2525 — SUBMIT, AUTH PLAIN, STARTTLS.
HMAC-SHA256 signed, replayable, idempotent. Reach any HTTPS endpoint you control.
Postfix-backed receive, parsed and stored against the matching tenant in real time.
Sign-in, orgs, member invites, magic links — all handled by Clerk. No password tables.
RFC 5545 invites generated, signed, and threaded against the conversation they belong to.
Every inbound mail walks the same six stops on its way to your inbox. No proprietary black boxes, no opaque "magic" — just well-understood pieces wired together carefully.
Every step is independently observable, retried with backoff, and bound to your tenant's schema. Outbound mail walks the same stops in reverse, with the queue handling delivery, webhooks, and domain warm-up scheduling.
Sending email shouldn't mean stitching together a transactional API, a newsletter tool, an inbox, and an analytics dashboard — and paying for the seams.
Koltrix is one product with one auth, one bill, and one source of truth for every message your business sends or receives. Built for teams who'd rather solve their customer's problem than wire up email plumbing.
A free tier you can stay on while you validate. Pay when the volume justifies it — never before.
100 sends a day, free, forever. Self-host any time. No credit card required.