def reject_notification_email(speech)
    speech.reject_mail_sent!
    liquid_template = prepare(speech.conference, __method__, {"speech" => speech, "topic" => speech.topic, "conference" => speech.conference})
    emails = speech.topic.speakers.collect(&:user).collect(&:email).join(",")
    mail(reply_to: speech.conference.email, to: emails, subject: liquid_template.subject, body: liquid_template.body)