Sendgrid
A cloud-based SMTP provider that allows you to send emails without having to maintain email servers
A service that provides solutions relating to marketing and/or transactional email and/or SMS.
Sendinblue API is a free Email API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
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Details from developers.brevo.com.

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Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
A cloud-based SMTP provider that allows you to send emails without having to maintain email servers
Email for AI agents: send email, receive replies as threads, with per-key send limits and approvals
EU-hosted email API for transactional and marketing email, with contacts, broadcasts, and analytics
The Sendinblue API is provided by Brevo API Documentation (developers.brevo.com). Build integrations with the Brevo API
Yes. The Sendinblue API is listed in the Email category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The Sendinblue API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the Sendinblue API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Sendinblue API is served over HTTPS, so it's safe to use in production.