Email APIs Side projects
Transactional email APIs for a side project
Password resets, signup confirmations, receipts. Every side project needs to send email, and every vendor's pricing page is designed to look cheaper than it is. Here is what the plans actually give you.
Affiliate disclosure
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Research basis: this guide is docs-based research, not hands-on load testing. Prices below come from each vendor's public pricing page as reported in third-party comparisons checked September-October 2026. Prices change; confirm on the vendor's page before committing. Last updated: October 2026.
The short answer
Just starting out, low volume: Resend's free tier (3,000 emails a month) is the easiest path from zero to sending. Watch the 100-per-day cap.
You care most about landing in the inbox: Postmark ($15 a month for 10,000 emails). You pay a premium; the premium buys deliverability focus.
Cheapest at serious scale: Amazon SES, if you can live with its setup friction. Note: new signups no longer get the old free tier (reported July 2026).
The comparison
| Provider | Free tier | Entry paid plan | Cost at ~50k emails/mo | The catch |
|---|---|---|---|---|
| Resend | 3,000/mo, hard cap of 100/day, 1 domain | $20/mo for 50,000 emails ($0.90 per 1k overage) | $20 | The 100/day cap is the real free tier. One busy day of order confirmations and you are done. Marketing email is a separate product billed by contacts. |
| Postmark | 100/mo (developer testing only) | $15/mo for 10,000 emails ($1.80 per 1k overage on Basic) | ~$63-90 depending on tier and overage rate | No real free tier for production; you upgrade before email 101. Transactional and broadcast streams are kept separate, which is why teams pay the premium. |
| Mailgun | ~3,000/mo (100/day) | $15/mo Basic for 10,000 emails; $35 Foundation; $90 Scale | $35 (Foundation) | Email validation is a separate paid add-on, not included. Overage is $1.30 per 1k on Foundation. |
| SendGrid | None. 60-day trial at 100/day only. | $19.95/mo Essentials (50k emails) | ~$20-35 | No permanent free tier at all, which surprises people who remember the old one. Dedicated IPs require the $89.95/mo Pro plan regardless of volume. |
| Brevo | 300 emails/day, no card | Starter from $9/mo | ~$69 (Starter, per comparisons) | The highest daily free send of the group. Starter pricing is a sliding scale; check the current ladder before assuming the $9 figure covers your volume. |
| Amazon SES | None for new signups (old free tier discontinued July 2026, reported) | Pay as you go, ~$0.16 per 1k emails (Essentials) | ~$8 | Cheapest raw price, most setup friction: sandbox mode, production access requests, and you build your own bounce handling. Headline rate looks cheap until you add deliverability add-ons. |
| Mailtrap | 4,000/mo (150/day) for the sending API; sandbox for staging | $20/mo Basic | $20 | Best known as a staging/testing inbox. Fine as a cheap sender, but it is really two products sharing a pricing page; know which one you are buying. |
How to choose
- Pre-launch / tiny volume: Resend free or Brevo free. Resend has the nicer developer experience (React Email templates, clean API); Brevo gives you more daily headroom.
- Transactional mail that must arrive: Postmark. The price per email is higher and it stays higher at scale. That is the trade, stated plainly.
- High volume, thin margins: Amazon SES. Budget a day of setup pain and read the sandbox docs before you promise anyone a launch date.
- Newsletters to an audience (different job): this guide is about transactional email. For newsletters, consider a dedicated newsletter tool like Kit (formerly ConvertKit) [affiliate link pending approval, currently direct].
What we could not verify
- Real-world inbox placement rates for each provider (we did not run seed-list tests).
- Exact current overage math on every tier; vendors change these quietly. We linked the vendor pages so you can check.
- Whether Resend runs a public affiliate program (we found none listed; links here are direct).
Sources: vendor pricing pages via third-party comparisons (ilounge.com, lettr.com, emailsoftwareinsights.com, apicostcalc.com), checked September-October 2026.