Improved References-Header follow up check.

app/models/channel/filter/follow_up_check.rb

@@ -54,11 +54,9 @@ module Channel::Filter::FollowUpCheck
       end
       if references != ''
         message_ids = references.split(/\s+/)
-        sender_type_agent = Ticket::Article::Sender.lookup(name: 'Agent')
-        sender_type_system = Ticket::Article::Sender.lookup(name: 'System')
         message_ids.each {|message_id|
           message_id_md5 = Digest::MD5.hexdigest(message_id)
-          article = Ticket::Article.where(message_id_md5: message_id_md5, sender_id: [sender_type_agent.id, sender_type_system.id]).order('created_at DESC, id DESC').limit(1).first
+          article = Ticket::Article.where(message_id_md5: message_id_md5).order('created_at DESC, id DESC').limit(1).first
           next if !article
           Rails.logger.debug "Follow up for '##{article.ticket.number}' in references."
           mail[ 'x-zammad-ticket-id'.to_sym ] = article.ticket_id

test/unit/email_process_follow_up_test.rb

@@ -127,6 +127,48 @@ no reference "
     assert_not_equal(ticket.id, ticket_p.id)
   end
 
+  test 'process with follow up check with two external reference headers' do
+
+    setting_orig = Setting.get('postmaster_follow_up_search_in')
+    Setting.set('postmaster_follow_up_search_in', %w(body attachment references))
+
+    data1 = "From: me@example.com
+To: z@example.com
+Subject: test 123
+Message-ID: <9d16181c-2db2-c6c1-ff7f-41f2da4e289a@linuxhotel.de>
+
+test 123
+"
+    ticket_p1, article_p1, user_p1 = Channel::EmailParser.new.process({}, data1)
+
+    sleep 1
+
+    data1 = "From: me@example.com
+To: z@example.com
+Subject: test 123
+Message-ID: <9d16181c-2db2-c6c1-ff7f-41f2da4e289a@linuxhotel.de>
+
+test 123
+"
+    ticket_p2, article_p2, user_p2 = Channel::EmailParser.new.process({}, data1)
+    assert_not_equal(ticket_p1.id, ticket_p2.id)
+
+    data2 = "From: you@example.com
+To: y@example.com
+Subject: RE: test 123
+Message-ID: <oknn9teOke2uqbFQdGj2umXUwTkqgu0CqWHkA6V4K8p@akmail>
+References: <9d16181c-2db2-c6c1-ff7f-41f2da4e289a@linuxhotel.de>
+
+test 123
+"
+    ticket_p3, article_p3, user_p3 = Channel::EmailParser.new.process({}, data2)
+
+    assert_equal(ticket_p2.id, ticket_p3.id)
+
+    Setting.set('postmaster_follow_up_search_in', setting_orig)
+
+  end
+
   test 'process with follow up check - with auto responses and no T# in subject_build' do
 
     ticket = Ticket.create(