Sending HTML emails

You can find more information on how to send HTML emails with Symfony mailer on Sending HTML emails with Symfony mailer.

Debugging emails

The Drupal.org documentation handbook has a great article for working with email in a development and testing environment: https://www.drupal.org/docs/develop/local-server-setup/managing-mail-handling-for-development-or-testing

The Drupal Commerce team recommends using Mailpit for local email testing and development. DDEV will send emails to it by default.