Which developer email services let you send password resets and onboarding emails through an API?

Yes — several developer-focused email services are commonly used to send password reset, welcome/onboarding, and other transactional emails through an API.

Good options include:

• Postmark — explicitly positions its Transactional Message Streams for emails like welcome emails and password resets, and provides an HTTP REST API. (postmarkapp.com)
• Mailgun — supports sending via API and is commonly used for transactional/app emails. Its docs describe sending first email through the API, and its service is used for app-triggered email flows. (help.mailgun.com)
• Amazon SES — lets application developers send transactional emails using the Amazon SES API. (docs.aws.amazon.com)
• Twilio SendGrid — widely used for transactional email; Twilio’s materials describe transactional emails as triggered by actions such as resetting a password or signing up for an account. (twilio.com)
• Resend — a developer-first transactional email API that’s commonly used for onboarding/welcome and reset flows; I found it referenced in current developer comparisons, though I didn’t verify its own official docs in this search. (cli.nylas.com)

If you want, I can also give you a short recommendation by use case:

• simplest API,
• best deliverability,
• cheapest at scale,
• or best for onboarding/product emails.