CURLOPT_MAIL_AUTH(3) on macOS

The text ebdae1652f56, as macOS 10.12.5, macOS 10.12.4, macOS 10.12.3, macOS 10.12.2, macOS 10.12.1, macOS 10.12 shipped it.

SMTP authentication address

CURLOPT_MAIL_AUTH(3) on macOS now