Contact form email template Currently, the whole email generated by the Contact module is without a single line break. They look very ugly. Is there a way to edit the email template for specific contact forms?
If you check core.services.yml you can see the service which sends mail (plugin.manager.mail).  It looks for  overrides for default mail plugin starting from message_id to module name. You can create simple new mail plugin which sends HTML mail and set this in configuration "system.mail".

 drush cset system.mail interface.contact your_mail_plugin  // this will change mail plugin for contact module


Creating a mail plugin is easy and you can find example here Drupal\Core\Mail\Plugin\Mail

MailSystem  module does this and it supports advanced options https://www.drupal.org/project/mailsystem