How to Architect a Modern Transactional Email System (Without the Bloat)

A funny thing about transactional email: everyone treats it like this heavyweight problem that needs a heavyweight stack. If you Google around, half the advice out there makes it sound like you need half of AWS plus a PhD in SMTP to send a password reset. You don’t.

A modern transactional email system isn’t complicated. It just needs to be predictable, fast, and as boring as possible. Boring is good. Boring is reliable. Boring doesn’t page you at 3 a.m. Here’s how I’d architect a transactional email system today, the same way I’ve built it for real products, minus all the unnecessary ceremony.

Start with the only thing that actually matters: delivering reliably

When you strip it down, transactional email has one job: Make sure the user gets the damn email. Everything else is decoration. That means:

• stay out of shared IP pools
• keep a consistent sending domain
• keep bounce/complaint rates low
• warm up slowly
• don’t mix transactional with blasts

There’s nothing glamorous here. Just discipline and basic hygiene. Once you do those things, the “architecture” becomes more about constraint than creativity.

Step 1: Use AWS SES as the delivery engine

You can swap in another provider if you want, but SES is the simplest, cheapest, and most stable option. It doesn’t pretend to be anything more than it is — a reliable pipe.

Why SES?

• predictable cost
• no aggressive markups
• straightforward API
• regional redundancy
• reputation controlled per account

Most people don’t realize SES handles a massive portion of the internet’s transactional email already — you just don’t see its name on the dashboard because vendors wrap it. You might as well use the source.

Step 2: Put a proper API layer in front of it

Don’t send directly from SES in your app. That path leads to slow deployments, messy SDK calls scattered around your codebase, and 2 a.m. debugging sessions where you end up reading raw AWS error messages.

You want a thin API layer upfront. It can be:

• FastAPI
• Hono
• Express (if you like pain)
• Go net/http (if you like simplicity)

All you need it to do:

• accept email requests
• validate payloads
• fetch templates
• render with variables
• talk to SES
• log events

That’s it. Keep it small enough that a single engineer can hold the entire mental model.

Step 3: Use a simple templating engine you won’t hate later

You don’t need a drag-and-drop builder. You don’t need a visual editor with 98 knobs.

You need:

• a real templating language
• HTML/CSS that isn’t awful
• support for variables and conditionals
• something you can hand off to engineers or designers

Liquid + MJML is plenty. Use Markdown if you want to be spartan. Just avoid building a whole WYSIWYG system unless you enjoy maintenance debt.

Step 4: Track the basics (and stop there)

Transactional email isn’t an analytics business. You only need:

• opens
• clicks
• bounces
• complaints
• delivery confirmations

Anything beyond that is vanity. If you’re doing A/B testing on password resets, you’ve gone off the rails. Hook in SES notifications, store the important bits, and don’t overthink it.

Step 5: Store logs — but don’t overbuild a logging platform

Log the essentials:

• request → email sent
• SES response
• message ID
• open/click tracking events
• bounce/complaint metadata

Doesn’t need Elasticsearch. Doesn’t need Kafka. Doesn’t need a dashboard with 12 filters. SQLite or Postgres is fine. In email, the worst bugs are almost always obvious if you have timestamps and SES IDs. Everything beyond that is nice to have, not critical.

Step 6: Add a retry and throttle layer

This part saves you more pain than anything:

• exponential backoff
• respect SES max send rate
• retry on 4xx/5xx
• stop retrying on hard bounces

Most transactional email failures aren’t dramatic. They’re just temporary blocks or throttling. Automatic retries turn 90% of those into non-issues.

Step 7: Keep your architecture embarrassingly simple

If your system looks like this:

app → email API → SES → user inbox

you’ve done it right.

If your system looks like this:

app → internal queue → worker pool → template compiler → microservice hub → event bus → delivery orchestrator → analytics cluster → sending node → SES → user inbox

you’ve built a resume item, not a reliable email pipeline.

Complexity does not improve deliverability. Consistency does.

Step 8: Resist the urge to add shiny features

Every team building email infra eventually reaches the same fork in the road:

• “Should we add marketing features?”
• “Should we build sequences?”
• “Should users upload lists?”
• “Should we support A/B tests?”

If your goal is transactional email, the answer is almost always no.

More features = more edge cases = more ways to hurt your own reputation.

Transactional email works best when it stays in its own lane.

Why this matters

A modern transactional email system doesn’t need to be impressive. It needs to be stable, cheap, predictable, and boring enough that it never becomes a problem. If I had to summarize the whole blueprint in one sentence: Keep the system simple enough that you can explain the full architecture to a junior engineer in under 10 minutes. If you can do that, everything else falls into place.

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A founder’s blueprint for building a modern transactional email system without unnecessary complexity. Practical advice on SES, API layers, templates, deliverability, and architecture that actually scales.

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