These classes provide optional additional functions to PHPMailer.
These are not loaded by the PHPMailer autoloader, so in some cases you may need to require them yourself before using them.
This class was originally written by Manuel Reinhard and provides a simple means of generating ICS/vCal files that are used in sending calendar events. PHPMailer does not use it directly, but you can use it to generate content appropriate for placing in the Ical property of PHPMailer. The PHPMailer project is now its official home as Manuel has given permission for that and is no longer maintaining it himself.
This class by Konstantin Riabitsev and Jim Jagielski implements HTML filtering to remove potentially malicious tags, such as <script> or onclick= attributes that can result in XSS attacks. This is a simple filter and is not as comprehensive as HTMLawed or HTMLPurifier, but it's easier to use and considerably better than nothing! PHPMailer does not use it directly, but you may want to apply it to user-supplied HTML before using it as a message body.
This class by Manuel Lemos (bundled with permission) adds the ability to authenticate with Microsoft Windows mail servers that use NTLM-based authentication. It is used by PHPMailer if you send via SMTP and set the AuthType property to NTLM; you will also need to use the Realm and Workstation properties. The original source is here.