diff --git a/app/presenters/messages/search_data_presenter.rb b/app/presenters/messages/search_data_presenter.rb
index 7a6260686..e90c9b600 100644
--- a/app/presenters/messages/search_data_presenter.rb
+++ b/app/presenters/messages/search_data_presenter.rb
@@ -39,7 +39,8 @@ class Messages::SearchDataPresenter < SimpleDelegator
   end
 
   def content_attributes_data
-    email_subject = content_attributes.dig(:email, :subject)
+    email_subject = content_attributes.dig(:email, :subject).presence ||
+                    conversation.additional_attributes&.dig('mail_subject').presence
     return {} if email_subject.blank?
 
     { email: { subject: email_subject } }
diff --git a/spec/presenters/messages/search_data_presenter_spec.rb b/spec/presenters/messages/search_data_presenter_spec.rb
index 7b3d4acb9..48faec12a 100644
--- a/spec/presenters/messages/search_data_presenter_spec.rb
+++ b/spec/presenters/messages/search_data_presenter_spec.rb
@@ -58,6 +58,35 @@ RSpec.describe Messages::SearchDataPresenter do
       end
     end
 
+    context 'when the message has no email subject but the conversation has a mail_subject' do
+      before do
+        conversation.update!(additional_attributes: { 'mail_subject' => 'Conversation Subject' })
+      end
+
+      it 'falls back to the conversation mail_subject' do
+        content_attrs = presenter.search_data[:content_attributes]
+        expect(content_attrs[:email][:subject]).to eq('Conversation Subject')
+      end
+    end
+
+    context 'when both the message email subject and conversation mail_subject are set' do
+      before do
+        conversation.update!(additional_attributes: { 'mail_subject' => 'Conversation subject' })
+        message.update!(content_attributes: { email: { subject: 'Message subject' } })
+      end
+
+      it 'prefers the message-level email subject' do
+        content_attrs = presenter.search_data[:content_attributes]
+        expect(content_attrs[:email][:subject]).to eq('Message subject')
+      end
+    end
+
+    context 'when neither message nor conversation has an email subject' do
+      it 'omits the email subject from content_attributes' do
+        expect(presenter.search_data[:content_attributes]).to eq({})
+      end
+    end
+
     context 'with campaign and automation data' do
       before do
         message.update(