valid_email_checker

https://github.com/johncallahan/valid_email_checker

valid_email_checker embeds the Rust crate check-if-email-exists and exposes it to Ruby as a native extension. It validates syntax, looks up MX records, holds an SMTP conversation with the recipient's mail exchanger, and reports disposable, role-based and catch-all addresses -- all in-process, with no HTTP service to run and no mail actually sent.