В портах нашел
`Mail::Verify' provides a function CheckAddress function for verifying email addresses. First the syntax of the email address is checked, then it verifies that there is at least one valid MX server accepting email for the domain. Using the Net::DNS manpage and the IO::Socket manpage a list of MX records (or, falling back on a hosts A record) are checked to make sure at least one SMTP server is accepting connections.

Как это дело привязать к sendmail? Или может есть другие пути типичного решения?