EVA
Validate email addresses
Disposable temporary Email addresses.
Guerrilla Mail API is a free Email API that requires no API key, is served over HTTPS and has unconfirmed CORS support.
Details from guerrillamail.com.

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Validate email addresses
Validate email syntax and MX, detect disposable/role addresses, suggest typo fixes
The Guerrilla Mail API is provided by Guerrilla Mail API (guerrillamail.com).
Yes. The Guerrilla Mail 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.
No. The Guerrilla Mail API requires no authentication, so you can start making requests without signing up.
CORS support for the Guerrilla Mail API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Guerrilla Mail API is served over HTTPS, so it's safe to use in production.