Sending, receiving, and organizing email in Outlook.com
Sorry to hear that you are having trouble receiving emails from this sender. If you have already added the sender's email address to your Safe Senders list and the messages are still not arriving, it is possible that the emails are being filtered before they reach your mailbox.
In this situation, the sender will need to review their email delivery status and contact Outlook.com Sender Support, as Microsoft provides specific assistance for senders experiencing delivery issues to Outlook.com, Hotmail, Live, or MSN addresses:
https://support.microsoft.com/en-us/outlook/sender-support-in-outlook-com
They may need to check their sending reputation, authentication settings, or whether their mail servers are being blocked by Outlook.com filtering systems.