Do follow up detection also with references header and comparing subject per default.

app/models/application_model/assets.rb

@@ -31,9 +31,10 @@ returns
     end
 
     return data if !self['created_by_id'] && !self['updated_by_id']
+    app_model_user = User.to_app_model
     %w(created_by_id updated_by_id).each { |local_user_id|
       next if !self[ local_user_id ]
-      next if data[ User.to_app_model ] && data[ User.to_app_model ][ self[ local_user_id ] ]
+      next if data[ app_model_user ] && data[ app_model_user ][ self[ local_user_id ] ]
       user = User.lookup(id: self[ local_user_id ])
       next if !user
       data = user.assets(data)

app/models/channel/filter/follow_up_check.rb

@@ -65,5 +65,44 @@ module Channel::Filter::FollowUpCheck
       end
     end
 
+    # get ticket# from references current email has same subject as inital article
+    if !mail[:subject].empty?
+
+      # get all references 'References' + 'In-Reply-To'
+      references = ''
+      if mail[:references]
+        references += mail[:references]
+      end
+      if mail['in-reply-to'.to_sym]
+        if references != ''
+          references += ' '
+        end
+        references += mail['in-reply-to'.to_sym]
+      end
+      if references != ''
+        message_ids = references.split(/\s+/)
+        message_ids.each { |message_id|
+          message_id_md5 = Digest::MD5.hexdigest(message_id)
+          article = Ticket::Article.where(message_id_md5: message_id_md5).order('created_at DESC, id DESC').limit(1).first
+          next if !article
+          ticket = article.ticket
+          next if !ticket
+          article_first = ticket.articles.first
+          next if !article_first
+
+          # remove leading "..:\s" and "..[\d+]:\s" e. g. "Re: " or "Re[5]: "
+          subject_to_check = mail[:subject]
+          subject_to_check.gsub!(/^(..(\[\d+\])?:\s)+/, '')
+
+          # if subject is different, it's no followup
+          next if subject_to_check != article_first.subject
+
+          Rails.logger.debug "Follow up for '##{article.ticket.number}' in references with same subject as inital article."
+          mail[ 'x-zammad-ticket-id'.to_sym ] = article_first.ticket_id
+          return true
+        }
+      end
+    end
+
   end
 end

test/unit/email_process_follow_up_test.rb

@@ -257,4 +257,69 @@ Some Text"
     assert_equal('open', ticket.state.name)
   end
 
+  test 'process with follow up check - ticket initiated by customer without T# in subject and other people in Cc reply to all' do
+
+    # check if follow up based on inital system sender address
+    setting_orig = Setting.get('postmaster_follow_up_search_in')
+    Setting.set('postmaster_follow_up_search_in', [])
+
+    subject = "ticket initiated by customer without T# in subject and other people in Cc reply to all #{rand(9999)}"
+
+    email_raw_string = "From: me@example.com
+To: my@system.test, bob@example.com
+Subject: #{subject}
+Message-ID: <123456789-$follow-up-test§-1@linuxhotel.de>
+
+Some Text"
+
+    ticket_p1, article_1, user_1, mail = Channel::EmailParser.new.process({}, email_raw_string)
+    ticket1 = Ticket.find(ticket_p1.id)
+    assert_equal(subject, ticket1.title)
+
+    # follow up possible because same subject
+    email_raw_string = "From: bob@example.com
+To: my@system.test, me@example.com
+Subject: AW: #{subject}
+Message-ID: <123456789-$follow-up-test§-2@linuxhotel.de>
+References: <123456789-$follow-up-test§-1@linuxhotel.de>
+
+Some Text"
+
+    ticket_p2, article_p2, user_p2, mail = Channel::EmailParser.new.process({}, email_raw_string)
+    ticket2 = Ticket.find(ticket_p2.id)
+    assert_equal(ticket1.id, ticket2.id)
+    assert_equal(subject, ticket2.title)
+
+    # follow up possible because same subject
+    email_raw_string = "From: bob@example.com
+To: my@system.test, me@example.com
+Subject: AW: RE: #{subject}
+Message-ID: <123456789-$follow-up-test§-2@linuxhotel.de>
+References: <123456789-$follow-up-test§-1@linuxhotel.de>
+
+Some Text"
+
+    ticket_p3, article_p3, user_p3, mail = Channel::EmailParser.new.process({}, email_raw_string)
+    ticket3 = Ticket.find(ticket_p3.id)
+    assert_equal(ticket1.id, ticket3.id)
+    assert_equal(subject, ticket3.title)
+
+    # follow up not possible because subject has changed
+    subject = "new subject without ticket ref #{rand(9_999_999)}"
+    email_raw_string = "From: bob@example.com
+To: my@system.test
+Subject: #{subject}
+Message-ID: <123456789-$follow-up-test§-3@linuxhotel.de>
+References: <123456789-$follow-up-test§-1@linuxhotel.de>
+
+Some Text"
+
+    ticket_p4, article_p4, user_p4, mail = Channel::EmailParser.new.process({}, email_raw_string)
+    ticket4 = Ticket.find(ticket_p4.id)
+    assert_not_equal(ticket1.id, ticket4.id)
+    assert_equal(subject, ticket4.title)
+
+    Setting.set('postmaster_follow_up_search_in', setting_orig)
+  end
+
 end