There has been some confusion on why PM have not been working. Well the problem has been discovered. The difference between your sentbox and your outbox is that sentbox is mail that you sent and the person you have sent it to has read it, whereas outbox is unread mail. Therefore if you delete your outbox mail then it will be deleted from their inbox and they will never read it.
So people who have sent me their fighters info but then deleted the mail in their outbox it means that I never received the info.