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Disposable Email.
Mailsac API is a free Test Data API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
Receive test emails with confidence. Mailsac is an API and service for quality assurance testing with disposable email accounts.
Details from mailsac.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.
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Zero-auth REST endpoints for mock user profiles, UUIDs and HTTP status codes
The Mailsac API is provided by Mailsac API Specification (mailsac.com). Receive test emails with confidence. Mailsac is an API and service for quality assurance testing with disposable email accounts.
Yes. The Mailsac API is listed in the Test Data 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 Mailsac API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the Mailsac API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Mailsac API is served over HTTPS, so it's safe to use in production.