Fixes #3824 - Email address not shown inside forwarded email

app/assets/javascripts/app/lib/app_post/full_quote_header.coffee

@@ -28,7 +28,7 @@ class App.FullQuoteHeader
 
   @fullQuoteHeaderForwardTo: (article) ->
     if article.type.name is 'email' || article.type.name is 'web'
-      @fullQuoteHeaderEnsurePrivacy(article.to) || article.to
+      @fullQuoteHeaderEnsureMultiPrivacy(article.to)
     else if article.sender.name is 'Customer' && article.type.name is 'phone'
       if email_address_id = App.Group.findByAttribute('name', article.to)?.email_address_id
         App.EmailAddress.find(email_address_id).displayName()
@@ -36,15 +36,17 @@ class App.FullQuoteHeader
         article.to
     else if article.sender.name is 'Agent' && article.type.name is 'phone'
       ticket = App.Ticket.find article.ticket_id
-      @fullQuoteHeaderEnsurePrivacy(ticket.customer_id) || @fullQuoteHeaderEnsurePrivacy(article.to) || article.to
+      @fullQuoteHeaderEnsurePrivacy(ticket.customer_id) || @fullQuoteHeaderEnsureMultiPrivacy(article.to)
     else
       article.to
 
   @fullQuoteHeaderForwardCC: (article) ->
     return if !article.cc
 
-    article
+    @fullQuoteHeaderEnsureMultiPrivacy(article.cc)
-      .cc
+
+  @fullQuoteHeaderEnsureMultiPrivacy: (input) ->
+    input
       .split(',')
       .map (elem) ->
         elem.trim()

spec/system/ticket/update/full_quote_header_spec.rb

@@ -21,7 +21,7 @@ RSpec.describe 'Ticket > Update > Full Quote Header', current_user_id: -> { curr
   context 'when "ui_ticket_zoom_article_email_full_quote_header" is enabled' do
     let(:full_quote_header_setting) { true }
 
-    it 'includes OP when forwarding' do
+    it 'includes sender when forwarding' do
       within(:active_content) do
         click_forward
 
@@ -31,7 +31,7 @@ RSpec.describe 'Ticket > Update > Full Quote Header', current_user_id: -> { curr
       end
     end
 
-    it 'includes OP when replying' do
+    it 'includes sender when replying' do
       within(:active_content) do
         highlight_and_click_reply
 
@@ -41,7 +41,7 @@ RSpec.describe 'Ticket > Update > Full Quote Header', current_user_id: -> { curr
       end
     end
 
-    it 'includes OP when article visibility toggled' do
+    it 'includes sender when article visibility toggled' do
       within(:active_content) do
         set_internal
         highlight_and_click_reply
@@ -55,7 +55,7 @@ RSpec.describe 'Ticket > Update > Full Quote Header', current_user_id: -> { curr
     context 'when customer is agent' do
       let(:customer) { create(:agent) }
 
-      it 'includes OP without email when forwarding' do
+      it 'includes sender without email when forwarding' do
         within(:active_content) do
           click_forward
 
@@ -66,13 +66,32 @@ RSpec.describe 'Ticket > Update > Full Quote Header', current_user_id: -> { curr
       end
     end
 
+    # https://github.com/zammad/zammad/issues/3824
+    context 'when TO contains multiple senders and one of them is a known Zammad user' do
+      let(:customer) { create(:customer) }
+      let(:to_1) { "#{customer.fullname} <#{customer.email}>" }
+      let(:to_2) { 'Example Two <two@example.org>' }
+
+      let(:ticket_article) { create(:ticket_article, ticket: ticket, to: [to_1, to_2].join(', ')) }
+
+      it 'includes all TO email address' do
+        within(:active_content) do
+          click_forward
+
+          within(:richtext) do
+            expect(page).to have_text(to_1).and(have_text(to_2))
+          end
+        end
+      end
+    end
+
     context 'ticket is created by agent on behalf of customer' do
       let(:agent)          { create(:agent) }
       let(:current_user)   { agent }
       let(:ticket)         { create(:ticket, group: group, title: 'Created by agent on behalf of a customer', customer: customer) }
       let(:ticket_article) { create(:ticket_article, ticket: ticket, from: 'Created by agent on behalf of a customer', origin_by_id: customer.id) }
 
-      it 'includes OP without email when replying' do
+      it 'includes sender without email when replying' do
         within(:active_content) do
           highlight_and_click_reply
 
@@ -87,7 +106,7 @@ RSpec.describe 'Ticket > Update > Full Quote Header', current_user_id: -> { curr
   context 'when "ui_ticket_zoom_article_email_full_quote_header" is disabled' do
     let(:full_quote_header_setting) { false }
 
-    it 'does not include OP when forwarding' do
+    it 'does not include sender when forwarding' do
       within(:active_content) do
         click_forward
 
@@ -97,7 +116,7 @@ RSpec.describe 'Ticket > Update > Full Quote Header', current_user_id: -> { curr
       end
     end
 
-    it 'does not include OP when replying' do
+    it 'does not include sender when replying' do
       within(:active_content) do
         highlight_and_click_reply