One App, Lot's of Email issues — So I Built Coldletter

For a while, Optogrid was quietly paying for and babysitting two separate email systems. One provider for transactional email (welcome messages, password resets, receipts) and a different platform for marketing (onboarding sequences, newsletters). Two dashboards, two bills, two mental models — for one small app. It would be fine if it was not painful…

This is the story of why I folded them into one tool, what I built, and where I think the same idea helps other people.

The pains I kept hitting

These weren’t hypothetical “wouldn’t it be nice” annoyances. They were the friction I felt every time I touched email.

Two systems for one app. Transactional lived behind one provider’s API. Marketing lived in a separate drag-and-drop platform. They didn’t know about each other. A user who unsubscribed in one place was still “active” in the other. Reporting was split in half. And I was paying twice to send email that a single provider’s API could already handle.

Hand-coding email that renders everywhere. MJML helps, but I was still hand-writing templates and crossing my fingers that they’d survive Gmail, Outlook, and dark mode. No versioning, no review, no diff. When I broke a template, I usually found out the same time a customer did.

Automation that fought me. Expressing something as simple as “on signup, send the welcome email, wait a day, then tag the user” took far more clicking than it should in a sprawling visual canvas. And when I hit a wall, I hit it hard — rigid plan limits and features I couldn’t bend to my use case. I even filed a bug with one of the tools at some point. Last I checked, it’s still open.

No real control. The honest version: I wanted email to feel like the rest of my codebase — typed, versioned, testable, in git. Instead it lived in someone else’s UI, behind someone else’s limits.

What I wanted instead

One API call to send anything, transactional or marketing.
Templates I version and test like code, with typed variables so a missing field fails loudly before it ships, not after.
Automations that read like logic, not a maze.
And the important one: keep my own provider. I didn’t want to replace SendGrid or SES — I wanted a layer on top of it. Bring your own key. Coldletter rides on your delivery; it doesn’t resell it back to you.

What I built

Coldletter started as Optogrid’s internal email service and grew into a standalone product. The shape of it:

Versioned MJML/HTML templates with typed variables and one-click test sends.
Campaigns — one-time bulk sends to a filtered audience.
Automations modeled as trigger → condition → action trees (on subscriber created, send X, wait, branch, tag) instead of a canvas you fight.
Compliance built in — one-click unsubscribe, bounce handling, provider webhooks. The unglamorous stuff you only notice when it’s missing.
An operator UI for the people who’d rather not touch the API.

On the light-stack note: a Fastify API with a Postgres-backed job queue (pg-boss) on Fly.io, a Next.js operator console on Vercel, Drizzle on the database, and MJML + Handlebars for rendering. Auth is better-auth — the same library I migrated to from Firebase on Optogrid.

What I learned

The boring parts are the hard parts. Cross-client rendering, plain-text fallbacks, one-click unsubscribe, bounce escalation — none of it is glamorous, all of it matters, and all of it is what the “just send email” tools quietly handle for you.
Postgres can be the whole backend. Running the job queue on Postgres instead of reaching for Redis kept the infrastructure small. For a solo build, fewer moving parts is worth a lot.
Building internal-first kept me honest. I generalized to multi-tenant and bring-your-own-key only after the thing was already earning its keep inside Optogrid. Solving my own problem first meant I never had to guess what actually mattered.

Opportunities for others

I built this for me, but the itch isn’t mine alone. It probably sounds familiar if:

You’re paying for a transactional provider and a separate marketing tool, and they don’t talk to each other.
You’ve outgrown an all-in-one platform’s limits but don’t want to rebuild delivery from scratch.
You want email templates and automations to live in version control, like everything else you ship.

If that’s you, we have the same problem, and Coldletter is my answer to it — take a look. And if you’re solving it a different way, I’d genuinely like to hear how.