I received the following email regarding the upcoming WordPress 5.5 release

A plugin you have commit access to has been flagged as using the PHPMailer library. This library has been updated in the upcoming WordPress release (5.5) from version 5.2.27 to version 6.1.6. This is a major update to the library with several backward compatibility breaks. The target date for the release of WordPress 5.5 is 2020-08-11.

Affected plugin(s):

• https://wordpress.org/plugins/stop-emails

Here are some rough code examples that may have matched in your plugin(s):

• $mailer = new PHPMailer();
• include ABSPATH . WPINC . 'class-phpmailer.php'

Trunk always contains the bleeding edge, unreleased WordPress code that is being worked on for the next release (in this case, 5.5). Please take the time to test your plugin(s) against trunk to ensure your users will not experience any issues or unintended behavior after this update.

• A full list of changes to the library: https://make.wordpress.org/core/2020/07/01/external-library-updates-in-wordpress-5-5-call-for-testing/
• The relevant changesets updating PHPMailer in WordPress: https://core.trac.wordpress.org/log/?revs=48033-48036,48058
• Official upgrade guide – Upgrading from PHPMailer 5.2 to 6.0: https://github.com/PHPMailer/PHPMailer/blob/master/UPGRADING.md#other-upgrade-changes

We need to test the plugin with WordPress 5.5 and make any necessary adjustments