A maintenance release with some small features:
- Added ability to inject custom address validators, and set the default validator
- Fixed TLS 1.2 compatibility
- Improved examples
- Improved Windows compatibility
- Upgraded DKIM signing to use SHA-2 hashes
- Fixed gmail XOAUTH2 scope
Note that (security patches notwithstanding) this will likely be the last release in the PHPMailer 5.2.x series for some time. The 6.0 branch will become master, and development will continue there, and any future 5.2.x releases will be in the 5.2-stable branch.