Mailfornet
Disposable inboxes for end-to-end signup tests, with long-polling and HMAC-signed webhooks
Verify email deliverability with a strict yes/no, disposable and catch-all detection.
MailRambo API is a free Email API that requires apiKey authentication, is served over HTTPS and does not support CORS, so it should be called from a server.
MailRambo email verification API docs: strict yes/no checks, a free sub-second mode for signup forms, batches, Node and Python SDKs, and 100 free verifications a month.
Details from mailrambo.com.

Unified API suite · now live
Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
Disposable inboxes for end-to-end signup tests, with long-polling and HMAC-signed webhooks
Check a domain's SPF, DKIM, DMARC and MX records and get what to fix, with the values to publish
Email API and SMTP for sending transactional and bulk emails, with email testing sandbox for safe development
The MailRambo API is provided by MailRambo (mailrambo.com). MailRambo email verification API docs: strict yes/no checks, a free sub-second mode for signup forms, batches, Node and Python SDKs, and 100 free verifications a month.
Yes. The MailRambo 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 MailRambo API uses apiKey authentication, so you need to register for credentials before making requests.
Not directly. The MailRambo API does not allow CORS, so call it from a server, serverless function or proxy instead of front-end JavaScript.
Yes. The MailRambo API is served over HTTPS, so it's safe to use in production.