What email API should I use for transactional emails from my app?

If you’re sending transactional emails from an app, the best choice is usually a dedicated email delivery service rather than a general marketing platform.

Good options

1) Postmark — best for pure transactional email

• Excellent deliverability
• Very clean API
• Great for password resets, receipts, alerts, verification emails
• Strong reputation for transactional-only sending

Best if: you want reliability and simplicity over lots of marketing features.

2) SendGrid — flexible and widely used

• Strong feature set
• Good API and SDK support
• Can handle both transactional and marketing emails
• Broad ecosystem and integrations

Best if: you want a general-purpose platform with lots of features.

3) Amazon SES — cheapest at scale

• Very low cost
• Highly scalable
• Good deliverability if configured well
• More setup and email-deliverability management required

Best if: cost matters most and you’re comfortable with a bit more setup.

4) Mailgun — developer-friendly

• Good APIs and logs
• Nice tooling for developers
• Solid for transactional sending

Best if: you want good developer ergonomics and flexibility.

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My recommendation

• Start with Postmark if your emails are mostly transactional and you care about deliverability.
• Use Amazon SES if you’re sending high volume and want the lowest cost.
• Use SendGrid if you want a broad, all-in-one option.

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What to look for

For transactional email APIs, prioritize:

• Deliverability
• Easy API/SDKs
• Webhooks for bounces/complaints/deliveries
• Logs and message search
• Domain authentication support: SPF, DKIM, DMARC
• Good template management
• Reasonable pricing

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Short answer

If you just want a recommendation: Postmark is often the best default choice for transactional emails from an app.

If you want, I can also give you a recommendation based on your stack, expected email volume, and budget.