Add new port mail/py-validate_email: Verifies if an email address is valid and really exists

Verifies and checks if an e-mail address is valid, properly formatted and really
exists. It can optionally check the MX records of the e-mail domain.

WWW: https://github.com/syrusakbary/validate_email

PR: 227029
Submitted by: Kai <freebsd_ports@k-worx.org>