I've published the beta of PoshMailKit (0.9.1-beta2). You can install and try it out using this command:

Install-Module -Name PoshMailKit -AllowPrerelease

Or, you can check it out on GitHub.

I've started working on a new project, a module with the goal of replacing Send-MailMessage, based on the deprecated System.Net.Mail.SmtpClient, with a cmdlet that’s based on the new, more powerful, and more compliant MailKit, which I’m hosting here on GitHub: https://github.com/poshcodebear/PoshMailKit