What is the best transactional email API?
Prices read from each vendor's own pricing page on 28 August 2026.
Transactional email is a different job from a newsletter and it goes wrong in a different way. Nobody notices it working. Everybody notices the password reset that never arrived, and by then the user has gone.
So the things worth paying for here are unglamorous: an API you can integrate in an afternoon, docs that answer the question you actually have, and a free tier that covers a real product's volume rather than a demo's. The one strategic question is whether you want marketing email in the same place, because that decision is expensive to reverse.
Our pick
Three thousand emails a month free, a clean API with real SDKs, React Email, and documentation that is the best in this category. Overage is pay-as-you-grow rather than a hard cliff. Two things to know: there is a hundred-a-day cap under that monthly figure, and there is no visual newsletter builder or list segmentation, because that is not what it is.
What we judged on
- Free monthly sending, and whether there is a daily cap underneath it
- Quality of the API and the docs
- Whether marketing and transactional live together or separately
- What happens at the plan boundary: overage, or a wall
Also worth it
Fully open source under AGPL-3.0 and self-hostable, with a thousand emails a month free on the hosted version and simple pay-per-email pricing with no seat fees. Transactional and marketing in one platform. Fewer templates and a smaller ecosystem than the incumbents.
The answer if you want one bill instead of two: transactional and marketing unified, every feature on every paid plan, API-first with React Email templates. A thousand contacts free. Monthly billing only with no annual discount, and contact pricing moves in large steps.
Prices, side by side
| Tool | From | Free tier |
|---|---|---|
| Resend | Free, then $20/mo | 3,000 emails/month, 100/day max, 3 domains, 5 AI credits/month |
| Plunk | Free | 1,000 emails/month free |
| Loops | Free, then $49/mo | Up to 1,000 subscribed contacts, 4,000 combined sends/month, full features, with a Loops footer |
Read on 28 August 2026. Every price change we have recorded.
Questions people ask
How many free transactional emails can I send?
Resend gives three thousand a month with a hundred-a-day cap. Plunk gives a thousand a month on its hosted plan and unlimited if you self-host it. Loops allows four thousand combined sends across a thousand contacts.
Can one tool do transactional and marketing email?
Loops and Plunk are both built for that, and it saves a bill and a second integration. Resend is deliberately transactional only, which is why its API is cleaner and its docs are shorter.
Who is responsible for deliverability?
You are, at every provider here. They give you the sending infrastructure and the authentication records; whether your mail lands in the inbox depends on your domain reputation and what you send. No tier upgrade fixes that.
This is one question about email marketing. See all 15 compared, or browse the other guides.