diff --git a/app/mailboxes/imap/imap_mailbox.rb b/app/mailboxes/imap/imap_mailbox.rb
index e57979048..27bc88e06 100644
--- a/app/mailboxes/imap/imap_mailbox.rb
+++ b/app/mailboxes/imap/imap_mailbox.rb
@@ -51,15 +51,17 @@ class Imap::ImapMailbox
   end
 
   def find_conversation_by_reference_ids
-    return if @inbound_mail.references.blank? && in_reply_to.present?
+    return if @inbound_mail.references.blank?
 
     message = find_message_by_references
-    conversation_from_message = @inbox.conversations.find(message.conversation_id) if message.present?
-
-    return conversation_from_message if conversation_from_message.present?
+    if message.present?
+      conversation = @inbox.conversations.find_by(id: message.conversation_id)
+      return conversation if conversation.present?
+    end
 
+    # FALLBACK_PATTERN use to find a conversation that is started by an agent (no incoming message yet)
     conversation_id = find_conversation_by_references
-    @inbox.conversations.find_by(uuid: conversation_id)
+    @inbox.conversations.find_by(uuid: conversation_id) if conversation_id.present?
   end
 
   def in_reply_to
diff --git a/spec/mailboxes/imap/imap_mailbox_spec.rb b/spec/mailboxes/imap/imap_mailbox_spec.rb
index 4535899cf..309a38a65 100644
--- a/spec/mailboxes/imap/imap_mailbox_spec.rb
+++ b/spec/mailboxes/imap/imap_mailbox_spec.rb
@@ -264,5 +264,54 @@ RSpec.describe Imap::ImapMailbox do
         expect(conversation.additional_attributes['in_reply_to']).to eq(multiple_in_reply_to_mail.in_reply_to.first)
       end
     end
+
+    context 'when a reply to a conversation started by an agent' do
+      let(:agent_conversation) { create(:conversation, account: account, inbox: channel.inbox, assignee: agent) }
+      let(:reply_mail_with_fallback_reference) do
+        # Simulate an email reply with a reference that matches FALLBACK_PATTERN
+        reference_id = "account/#{account.id}/conversation/#{agent_conversation.uuid}@chatwoot.com"
+        create_inbound_email_from_mail(
+          from: 'email@gmail.com',
+          to: 'imap@gmail.com',
+          subject: 'Re: Agent started conversation',
+          references: [reference_id]
+        )
+      end
+
+      it 'appends email to the existing conversation using FALLBACK_PATTERN' do
+        expect(agent_conversation.messages.size).to eq(0)
+
+        class_instance.process(reply_mail_with_fallback_reference.mail, channel)
+
+        agent_conversation.reload
+        expect(agent_conversation.messages.size).to eq(1)
+        expect(agent_conversation.messages.last.content_attributes['email']['from']).to eq(reply_mail_with_fallback_reference.mail.from)
+      end
+    end
+
+    context 'when references contain both message and fallback patterns' do
+      let(:agent_conversation) { create(:conversation, account: account, inbox: channel.inbox, assignee: agent) }
+      let(:reply_mail_with_multiple_references) do
+        # Multiple references including both patterns
+        fallback_reference = "account/#{account.id}/conversation/#{agent_conversation.uuid}@chatwoot.com"
+        other_reference = 'some-other-message-id@example.com'
+        create_inbound_email_from_mail(
+          from: 'email@gmail.com',
+          to: 'imap@gmail.com',
+          subject: 'Re: Multiple references',
+          references: [other_reference, fallback_reference]
+        )
+      end
+
+      it 'finds conversation using fallback pattern when message lookup fails' do
+        expect(agent_conversation.messages.size).to eq(0)
+
+        class_instance.process(reply_mail_with_multiple_references.mail, channel)
+
+        agent_conversation.reload
+        expect(agent_conversation.messages.size).to eq(1)
+        expect(agent_conversation.messages.last.content_attributes['email']['from']).to eq(reply_mail_with_multiple_references.mail.from)
+      end
+    end
   end
 end