class FollowerMailerService

  def self.send_live_effort_mail(participant_id, split_time_ids)
    live_effort_mail_data = LiveEffortMailData.new(participant_id, split_time_ids)
    live_effort_mail_data.followers.each do |follower|
      FollowerMailer.live_effort_email(follower, live_effort_mail_data.effort_data).deliver_later
    end
  end

end
class FollowerMailerService

  def self.send_live_effort_mail(participant_id, split_time_ids)
    live_effort_mail_data = LiveEffortMailData.new(participant_id, split_time_ids)
    live_effort_mail_data.followers.each do |follower|
      FollowerMailer.live_effort_email(follower, live_effort_mail_data.effort_data).deliver_now
    end
  end

end
--- 
+++ 
@@ -3,7 +3,7 @@
   def self.send_live_effort_mail(participant_id, split_time_ids)
     live_effort_mail_data = LiveEffortMailData.new(participant_id, split_time_ids)
     live_effort_mail_data.followers.each do |follower|
-      FollowerMailer.live_effort_email(follower, live_effort_mail_data.effort_data).deliver_now
+      FollowerMailer.live_effort_email(follower, live_effort_mail_data.effort_data).deliver_later
     end
   end
 
Change follower mail delivery to background task.
