What should I use if I need an API for onboarding emails and account alerts?

If you need an API specifically for onboarding emails and account alerts, you’ll usually want a transactional email service rather than a bulk marketing platform.

Good options:

• SendGrid — popular, reliable, easy API, good for transactional and notification emails.
• Mailgun — strong developer-friendly API, good deliverability and event tracking.
• Postmark — excellent for transactional emails, very reliable for alerts and onboarding flows.
• Amazon SES — cheaper at scale, but more setup and less out-of-the-box convenience.

If your main use case is:

• Onboarding emails: welcome messages, verification emails, password setup
• Account alerts: login alerts, billing notices, security notifications

then Postmark or SendGrid are usually the easiest places to start.

If you want, I can also recommend one based on your priorities like lowest cost, best deliverability, or easiest integration.