fix: search for nil in-reply-to messages (#7286)

app/mailboxes/imap/imap_mailbox.rb

@@ -35,9 +35,9 @@ class Imap::ImapMailbox
   end
 
   def find_conversation_by_in_reply_to
-    return if in_reply_to.blank? && @inbound_mail.references.blank?
+    return if in_reply_to.blank?
 
-    message = @inbox.messages.find_by(source_id: in_reply_to) || find_message_by_references
+    message = @inbox.messages.find_by(source_id: in_reply_to)
     if message.nil?
       @inbox.conversations.where("additional_attributes->>'in_reply_to' = ?", in_reply_to).first
     else
@@ -45,6 +45,16 @@ class Imap::ImapMailbox
     end
   end
 
+  def find_conversation_by_reference_ids
+    return if @inbound_mail.references.blank? && in_reply_to.present?
+
+    message = find_message_by_references
+
+    return if message.nil?
+
+    @inbox.conversations.find(message.conversation_id)
+  end
+
   def in_reply_to
     @inbound_mail.in_reply_to
   end
@@ -52,8 +62,6 @@ class Imap::ImapMailbox
   def find_message_by_references
     message_to_return = nil
 
-    return if @inbound_mail.references.blank?
-
     references = Array.wrap(@inbound_mail.references)
 
     references.each do |message_id|
@@ -64,18 +72,22 @@ class Imap::ImapMailbox
   end
 
   def find_or_create_conversation
-    @conversation = find_conversation_by_in_reply_to || ::Conversation.create!({ account_id: @account.id,
+    @conversation = find_conversation_by_in_reply_to || find_conversation_by_reference_ids || ::Conversation.create!(
-                                                                                 inbox_id: @inbox.id,
+      {
-                                                                                 contact_id: @contact.id,
+        account_id: @account.id,
-                                                                                 contact_inbox_id: @contact_inbox.id,
+        inbox_id: @inbox.id,
-                                                                                 additional_attributes: {
+        contact_id: @contact.id,
-                                                                                   source: 'email',
+        contact_inbox_id: @contact_inbox.id,
-                                                                                   in_reply_to: in_reply_to,
+        additional_attributes: {
-                                                                                   mail_subject: @processed_mail.subject,
+          source: 'email',
-                                                                                   initiated_at: {
+          in_reply_to: in_reply_to,
-                                                                                     timestamp: Time.now.utc
+          mail_subject: @processed_mail.subject,
-                                                                                   }
+          initiated_at: {
-                                                                                 } })
+            timestamp: Time.now.utc
+          }
+        }
+      }
+    )
   end
 
   def find_or_create_contact

spec/mailboxes/imap/imap_mailbox_spec.rb

@@ -79,6 +79,42 @@ RSpec.describe Imap::ImapMailbox do
       end
     end
 
+    context 'when a new conversation with nil in_reply_to' do
+      let(:prev_conversation) { create(:conversation, account: account, inbox: channel.inbox, assignee: agent) }
+      let(:reply_mail) do
+        create_inbound_email_from_mail(from: 'email@gmail.com', to: 'imap@gmail.com', subject: 'Hello!', in_reply_to: nil)
+      end
+
+      it 'appends new email to the existing conversation' do
+        create(
+          :message,
+          content: 'Incoming Message',
+          message_type: 'incoming',
+          inbox: inbox,
+          account: account,
+          conversation: prev_conversation
+        )
+        create(
+          :message,
+          content: 'Outgoing Message',
+          message_type: 'outgoing',
+          inbox: inbox,
+          source_id: nil,
+          account: account,
+          conversation: prev_conversation
+        )
+
+        expect(prev_conversation.messages.size).to eq(2)
+
+        class_instance.process(reply_mail.mail, channel)
+
+        expect(prev_conversation.messages.size).to eq(2)
+
+        new_converstion_message = Conversation.last.messages.last.content_attributes
+        expect(new_converstion_message['email']['subject']).to eq('Hello!')
+      end
+    end
+
     context 'when a reply for non existing email conversation' do
       let(:reply_mail) do
         create_inbound_email_from_mail(from: 'email@gmail.com', to: 'imap@gmail.com', subject: 'Hello!', in_reply_to: 'test-in-reply-to')