SMTPMailServerImpl Not Accessible for Plugins in Confluence > 9.0.0?

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Hello Everyone,

I have a plugin that works in confluence previously to 9.0.0. I am still able to compile the Plugin but when testing against some endpoints I run into issues. Primarily I am trying to run the following line:

 final SMTPMailServer smtpMailServer = mailServerManager.isDefaultSMTPMailServerDefined()
                ? mailServerManager.getDefaultSMTPMailServer()
                : new SMTPMailServerImpl.Builder<>().build();`

But I am greeted by the error

java.lang.NoClassDefFoundError: com/atlassian/mail/server/impl/SMTPMailServerImpl$Builder

Further research reveals that it is indeed not loadable (tested via)

Class.forName("com.atlassian.mail.server.impl.SMTPMailServerImpl$Builder", false, cl);

Now I have not found anything online about import com.atlassian.mail.server.impl.SMTPMailServerImpl; beeing no longer availiable in newer confluence version. Can anyone give me confirmation if this is indeed intended to be inaccessible to Plugins and is there a replacement alternative for it?