added services

services/app/models/application_record.rb

@@ -0,0 +1,3 @@
+class ApplicationRecord < ActiveRecord::Base
+  self.abstract_class = true
+end

services/app/models/mail_recipient.rb

@@ -0,0 +1,4 @@
+class MailRecipient < ApplicationRecord
+  belongs_to :received_mail
+  belongs_to :recipient
+end

services/app/models/received_mail.rb

@@ -0,0 +1,4 @@
+class ReceivedMail < ApplicationRecord
+  belongs_to :sender
+  has_many :mail_recipients
+end

services/app/models/recipient.rb

@@ -0,0 +1,3 @@
+class Recipient < ApplicationRecord
+  has_many :emails, foreign_key: :recipient_id, class_name: 'MailRecipient'
+end

services/app/models/sender.rb

@@ -0,0 +1,3 @@
+class Sender < ApplicationRecord
+  has_many :sent_mails, foreign_key: :sender_id, class_name: 'ReceivedMail'
+end