Deprecate module in favor of core's built in SMTP mail handling capabilities offered in 10.2.x

The added mailer plugin is a minimal implementation and experimental.

The core issue you commented on is part of 🌱 [META] Adopt the symfony mailer component Needs review which will completely revamp the mail API and *that* will then essentially make all existing mail plugin modules dead code. But there will still be a need to provide a UI for the mailer capabilities of core, which this project could provide, or https://www.drupal.org/project/symfony_mailer_lite → or https://www.drupal.org/project/symfony_mailer → , remains to be seen.

Right now, I wouldn't worry too much about that if you use smtp and it works for you.

Thanks for the additional context.

Like Berdir said -- likely we will just adopt the core functionality and put a UI on top of it.. which should make this code much cleaner. SMTP can provide an upgrade path for those using the existing system.