chore: Prevent notification email loop (#3386)

Configuring an agent email also as a support email inbox leads to conversations getting created in a loop if notifications were also configured to the same email.

app/mailboxes/mailbox_helper.rb

@@ -28,4 +28,9 @@ module MailboxHelper
     end
     @message.save!
   end
+
+  def notification_email_from_chatwoot?
+    # notification emails are send via mailer sender email address. so it should match
+    @processed_mail.original_sender == Mail::Address.new(ENV.fetch('MAILER_SENDER_EMAIL', 'Chatwoot <accounts@chatwoot.com>')).address
+  end
 end