Sending newsletters in HTML...no problem. Send them scheduled with Simplenews Scheduler and Swiftmailer.
There are some examples.
You can choose HTML
This module has to be installed with Composer (see contribution Composer). The module is dependent from the Mail System module. You can send HTML mails with it. Webform uses Swift Mailer.
This module is a basic mail module. Often used in combination with other modules like Swiftmailer.