Uses the oauth2-client package from the League of Extraordinary Packages.

Specifically for PHPMailer to use for RFC1939 POP-before-SMTP authentication. 1) This class does not support APOP authentication. 2) Opening and closing lots of POP3 connections can be quite slow. If you need to send a batch of emails then just perform the authentication once at the start, and then loop through your mail sending script. Providing this process doesn't take longer than the verification period lasts on your POP3 server, you should be fine. 3) This is really ancient technology; you should only need to use it to talk to very old systems. 4) This POP3 class is deliberately lightweight and incomplete, implementing just enough to do authentication. If you want a more complete class there are other POP3 classes for PHP available.

Implements RFC 821 SMTP commands and provides some utility methods for sending mail to an SMTP server.