test: fallback references condition

app/mailboxes/application_mailbox.rb

@@ -5,6 +5,7 @@ class ApplicationMailbox < ActionMailbox::Base
   # Eg: email should be something like : reply+6bdc3f4d-0bec-4515-a284-5d916fdde489@domain.com
   REPLY_EMAIL_UUID_PATTERN = /^reply\+([0-9a-f]{8}\b-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-\b[0-9a-f]{12})$/i
   CONVERSATION_MESSAGE_ID_PATTERN = %r{conversation/([a-zA-Z0-9-]*?)/messages/(\d+?)@(\w+\.\w+)}
+  CONVERSATION_FALLBACK_ID_PATTERN = %r{account/(\d+)/conversation/([a-zA-Z0-9-]+)@}
 
   # routes as a reply to existing conversations
   routing(
@@ -24,14 +25,27 @@ class ApplicationMailbox < ActionMailbox::Base
     # <account/#{@account.id}/conversation/#{@conversation.uuid}@#{@account.inbound_email_domain}>
     def in_reply_to_mail?(inbound_mail)
       in_reply_to = inbound_mail.mail.in_reply_to
+      references = inbound_mail.mail.references
 
-      in_reply_to.present? && (
+      # Check in_reply_to first
+      return true if in_reply_to.present? && (
         in_reply_to_matches?(in_reply_to) || Message.exists?(source_id: in_reply_to)
       )
+
+      # Fallback to checking references header
+      references.present? && references_match?(references)
     end
 
     def in_reply_to_matches?(in_reply_to)
-      Array.wrap(in_reply_to).any? { it.match?(CONVERSATION_MESSAGE_ID_PATTERN) }
+      Array.wrap(in_reply_to).any? { |id| id.match?(CONVERSATION_MESSAGE_ID_PATTERN) || id.match?(CONVERSATION_FALLBACK_ID_PATTERN) }
+    end
+
+    def references_match?(references)
+      Array.wrap(references).any? do |reference|
+        reference.match?(CONVERSATION_MESSAGE_ID_PATTERN) ||
+          reference.match?(CONVERSATION_FALLBACK_ID_PATTERN) ||
+          Message.exists?(source_id: reference)
+      end
     end
 
     # checks if follow this pattern  send it to reply_mailbox

app/mailboxes/reply_mailbox.rb

@@ -21,8 +21,10 @@ class ReplyMailbox < ApplicationMailbox
   def find_relative_conversation
     if @conversation_uuid
       find_conversation_with_uuid
-    elsif mail.in_reply_to.present?
-      find_conversation_with_in_reply_to
+    elsif mail.in_reply_to.present? || mail.references.present?
+      find_conversation_with_in_reply_to if mail.in_reply_to.present?
+      # If still no conversation found and references exist, try references as fallback
+      find_conversation_with_references if @conversation.blank? && mail.references.present?
     end
   end
 
@@ -79,6 +81,55 @@ class ReplyMailbox < ApplicationMailbox
     find_conversation_by_message_id(in_reply_to_addresses) if @conversation.blank?
   end
 
+  # Find conversation from References header as fallback
+  # Extract conversation UUID from any reference that matches our patterns
+  def find_conversation_with_references
+    references_addresses = mail.references
+    references_addresses = [references_addresses] if references_addresses.is_a?(String)
+
+    references_addresses.each do |reference|
+      conversation = find_conversation_from_reference(reference)
+      next unless conversation && conversation_belongs_to_channel?(conversation)
+
+      @conversation = conversation
+      @conversation_uuid = conversation.uuid
+      break
+    end
+  end
+
+  def find_conversation_from_reference(reference)
+    # Try message-specific pattern: conversation/{uuid}/messages/{id}@domain
+    message_match = reference.match(::ApplicationMailbox::CONVERSATION_MESSAGE_ID_PATTERN)
+    if message_match
+      uuid = message_match.captures[0]
+      conversation = Conversation.find_by(uuid: uuid)
+      return conversation if conversation.present?
+    end
+
+    # Try conversation fallback pattern: account/{id}/conversation/{uuid}@domain
+    fallback_match = reference.match(::ApplicationMailbox::CONVERSATION_FALLBACK_ID_PATTERN)
+    if fallback_match
+      uuid = fallback_match.captures[1]
+      conversation = Conversation.find_by(uuid: uuid)
+      return conversation if conversation.present?
+    end
+
+    # Try finding by message source_id
+    message = Message.find_by(source_id: reference)
+    message&.conversation
+  end
+
+  def conversation_belongs_to_channel?(conversation)
+    return true unless conversation
+
+    # Get the channel from the email's To/CC addresses
+    channel = EmailChannelFinder.new(mail).perform
+    return false unless channel
+
+    # Check if the conversation's inbox matches the channel
+    conversation.inbox.channel_id == channel.id
+  end
+
   def validate_resource(resource)
     Rails.logger.error "[App::Mailboxes::ReplyMailbox] Email conversation with uuid: #{conversation_uuid} not found" if resource.nil?
 

spec/mailboxes/reply_mailbox_spec.rb

@@ -248,5 +248,143 @@ RSpec.describe ReplyMailbox do
         )
       end
     end
+
+    context 'with references header' do
+      let(:reply_mail_with_references) { create_inbound_email_from_fixture('reply_mail_without_uuid.eml') }
+      let(:email_channel) { create(:channel_email, email: 'test@example.com', account: account) }
+      let(:conversation_1) do
+        create(
+          :conversation,
+          assignee: agent,
+          inbox: email_channel.inbox,
+          account: account,
+          additional_attributes: { mail_subject: "Discussion: Let's debate these attachments" }
+        )
+      end
+
+      before do
+        conversation_1.update!(uuid: '6bdc3f4d-0bec-4515-a284-5d916fdde489')
+      end
+
+      context 'with message-specific pattern in references' do
+        before do
+          reply_mail_with_references.mail['References'] = '<conversation/6bdc3f4d-0bec-4515-a284-5d916fdde489/messages/123@test.com>'
+        end
+
+        it 'finds conversation from references header with message pattern' do
+          described_class.receive reply_mail_with_references
+          expect(conversation_1.messages.last.content).to include("Let's talk about these images:")
+        end
+      end
+
+      context 'with conversation fallback pattern in references' do
+        before do
+          reply_mail_with_references.mail['References'] = "<account/#{account.id}/conversation/6bdc3f4d-0bec-4515-a284-5d916fdde489@test.com>"
+        end
+
+        it 'finds conversation from references header with fallback pattern' do
+          described_class.receive reply_mail_with_references
+          expect(conversation_1.messages.last.content).to include("Let's talk about these images:")
+        end
+      end
+
+      context 'with multiple references including conversation pattern' do
+        before do
+          reply_mail_with_references.mail['References'] = [
+            '<some-random-message-id@gmail.com>',
+            "<account/#{account.id}/conversation/6bdc3f4d-0bec-4515-a284-5d916fdde489@test.com>",
+            '<another-random-message-id@outlook.com>'
+          ].join("\r\n ")
+        end
+
+        it 'finds conversation from any reference in the chain' do
+          described_class.receive reply_mail_with_references
+          expect(conversation_1.messages.last.content).to include("Let's talk about these images:")
+        end
+      end
+
+      context 'with message source_id in references' do
+        before do
+          conversation_1.messages.create!(
+            source_id: 'original-message-id@test.com',
+            account_id: account.id,
+            message_type: 'outgoing',
+            inbox_id: email_channel.inbox.id,
+            content: 'Original message'
+          )
+          reply_mail_with_references.mail['References'] = '<original-message-id@test.com>'
+        end
+
+        it 'finds conversation from message source_id in references' do
+          described_class.receive reply_mail_with_references
+          expect(conversation_1.messages.last.content).to include("Let's talk about these images:")
+        end
+      end
+
+      context 'with conversation from different channel in references' do
+        let(:other_email_channel) { create(:channel_email, email: 'other@example.com', account: account) }
+        let(:other_conversation) do
+          create(
+            :conversation,
+            assignee: agent,
+            inbox: other_email_channel.inbox,
+            account: account
+          )
+        end
+
+        before do
+          other_conversation.update!(uuid: 'aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee')
+          reply_mail_with_references.mail['References'] = '<conversation/aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee/messages/456@test.com>'
+        end
+
+        it 'does not use conversation from different channel' do
+          described_class.receive reply_mail_with_references
+          expect(other_conversation.messages.count).to eq(0)
+        end
+      end
+
+      context 'when in_reply_to fails but references has valid conversation' do
+        before do
+          reply_mail_with_references.mail['In-Reply-To'] = '<non-existent-message-id@test.com>'
+          reply_mail_with_references.mail['References'] = "<account/#{account.id}/conversation/6bdc3f4d-0bec-4515-a284-5d916fdde489@test.com>"
+        end
+
+        it 'falls back to references header when in_reply_to lookup fails' do
+          described_class.receive reply_mail_with_references
+          expect(conversation_1.messages.last.content).to include("Let's talk about these images:")
+        end
+      end
+
+      context 'when in_reply_to fails and references has message pattern' do
+        before do
+          reply_mail_with_references.mail['In-Reply-To'] = '<random-invalid-id@gmail.com>'
+          reply_mail_with_references.mail['References'] = '<conversation/6bdc3f4d-0bec-4515-a284-5d916fdde489/messages/789@test.com>'
+        end
+
+        it 'falls back to references with message pattern when in_reply_to lookup fails' do
+          described_class.receive reply_mail_with_references
+          expect(conversation_1.messages.last.content).to include("Let's talk about these images:")
+        end
+      end
+
+      context 'when in_reply_to fails and references has message source_id' do
+        before do
+          conversation_1.messages.create!(
+            source_id: 'valid-message-id@test.com',
+            account_id: account.id,
+            message_type: 'outgoing',
+            inbox_id: email_channel.inbox.id,
+            content: 'Previous message'
+          )
+          reply_mail_with_references.mail['In-Reply-To'] = '<wrong-message-id@test.com>'
+          reply_mail_with_references.mail['References'] = '<valid-message-id@test.com>'
+        end
+
+        it 'falls back to references with source_id when in_reply_to lookup fails' do
+          described_class.receive reply_mail_with_references
+          expect(conversation_1.messages.last.content).to include("Let's talk about these images:")
+        end
+      end
+    end
   end
 end