| OAuthTokenProvider | OAuthTokenProvider - OAuth2 token provider interface. |
| Exception | PHPMailer exception handler. |
| OAuth | OAuth - OAuth2 authentication wrapper class. |
| PHPMailer | PHPMailer - PHP email creation and transport class. |
| POP3 | PHPMailer POP-Before-SMTP Authentication Class. |
| SMTP | PHPMailer RFC821 SMTP email transport class. |