asciinema.org/app/mailers/user_mailer.rb

class UserMailer < ActionMailer::Base
  default from: "ascii.io <hello@ascii.io>"

  def new_comment_email(user, comment)
    @comment = comment
    @author = comment.user
    @asciicast = AsciicastDecorator.new(@comment.asciicast)

    to = "~#{user.nickname} <#{user.email}>"
    subject = %(New comment for #{@asciicast.smart_title})
    mail :to => to, :subject => subject
  end
end