I'm sorry to hear that you're experiencing this issue. I'm happy to help.
Are you accessing Outlook through the web version, or the Outlook app on your computer, whether Classic or the new version?
Have you checked your Junk Email or Spam folder to see if the messages were filtered there?
Try sending a test email from the affected account to the email address in question. Did you receive it?
If not, and you receive an error message, please share the full error message here so I can take a closer look.
If the email was successfully sent, review your forwarding settings and blocked senders list.
Sign in to your Microsoft account using the link below and check whether your emails are being forwarded to another address. If forwarding is enabled and you do not want this, select the option to stop forwarding.
https://outlook.live.com/mail/0/options/mail/forwarding
Review your blocked senders list by going to Settings, then Mail, then Junk Email, and check the Blocked Senders section.
Also, make sure your mailbox has enough available storage, as a full mailbox can prevent you from sending or receiving messages.
You may also want to turn off Focused Inbox so all emails appear in a single view:
https://support.microsoft.com/office/focused-inbox-for-outlook-f445ad7f-02f4-4294-a82e-71d8964e3978
Consider adding the sender’s email address to your Safe Senders list to prevent Outlook from blocking or redirecting their messages: