mailer_idea.rb

MyApp.mailer :notifier do
  deafult :from => "[email protected]"

  email :registration do |name, surname, email|
    to email
    subject "Registration"
    content_type "text/plain"
    body render('notifier/registration')
  end

  email :comment do |account, post|
    to Account.administrators_emails
    subject "New comment on #{post.title}"
    body render('comments/preview', :layout => false)
  end
end

MyApp.rb

class MyApp < Padrino::Application

  mailer :accounts do
    deafult :from => "[email protected]"

    email :signup do |name, surname, email|
      to email
      subject "Registration"
      content_type "text/plain"
      body render('notifier/registration')
    end
  end

  contoller :accounts do

    post :signup do
      @account = Account.create(params[:account])
      ...
      Mailer.deliver(:accounts, :signup, :name => account.name, :surname => account.surname, :email => account.email)
    end
  end
end

Check out the issue for the work I have done to support this syntax with a nice dsl layer over the existing system: http://github.com/padrino/padrino-framework/issues/#issue/127