Register a template extension so mailer templates written in a templating language other than rhtml or rxml are supported. To use this, include in your template-language plugin’s init code or on a per-application basis, this can be invoked from config/environment.rb:

ActionMailer::Base.register_template_extension('haml')

Source Code

# File action_mailer/base.rb, line 393
def register_template_extension(extension)
  template_extensions << extension
end