Sending, receiving, and organizing email in Outlook.com
@Ifigeneia Moulinou said
I had done all the steps suggested by virtual support even before I have been told. Nothing works.
I understand your frustration. But unless you are in an IT Managed environment, where they can do a full message trace, there is just not anything you can do from your side.
When the Microsoft mail servers bounce a message destined for your account they are suppose to send a Non-Delivery Report (NDR) to the sender telling them why it couldn't be delivered. You have got to get your hands on one of those NDRs. (It may be in the sender's Junk/Spam folder). That is the only way you can know for sure that the other person actually sent the mail and why the Microsoft mail servers failed to deliver it.