Hello, thank you for reaching out to Microsoft Q&A.
What is the exact error message the sender receives when they email you?
Send a test email from another one of your accounts to the affected email address. Check whether you receive any bounce-back (non-delivery) error messages. If you receive an error in the outbox, please share the complete error message here.
If the email is sent successfully, then please check your email forwarding rules and blocked senders list, and verify whether the messages have been routed to another folder, such as Junk or Spam or forwarded to another email address.
Open any web browser (use incognito tab), Sign in with your Microsoft account here:
Email forwarding rules: https://outlook.live.com/mail/0/options/mail/forwarding
(Click Do not forward if your emails are being forwarded to another address)
Then, check your email Rules and Blocked senders lists.
Additionally, ensure you have enough mailbox storage space to send and receive emails.