Starting with version 2023.2, Adaxes uses a new library for email delivery. The old Microsoft library used in previous versions had an issue - if SSL was enabled in the Adaxes mail settings but your SMTP server did not support it, the result would be a silent fallback to TLS. In the new version, an error message is thrown instead.
Using the 465 port is a valid approach. However, we recommend clearing the corresponding option (The server requires an encrypted connection (SSL)) and specifying the 587 port in the Adaxes mail settings. It does not mean your mail will be sent unencrypted. If the 587 port is specified, Adaxes will use TLS, which is effectively an upgraded version of SSL with fixed security vulnerabilities.