I understand how frustrating this is, especially since you can still sign in but can no longer see the address and also cannot send or receive email.
Have you tried the Q&A Assist suggestions under your post? If yes, what happened?
To make sure I understand your situation correctly, could you please clarify these first:
- When you say you can't see your account in "the list of addresses", do you mean the email addresses/aliases linked to your Microsoft account, or a list inside Outlook.com?
- Are you still signing in with the same email address as before, or with a different one now?
- When you try to send or receive email, do you see any specific error message?
Once you confirm those details, it will be easier to identify whether this is an account alias issue or a mailbox/send-receive issue so I can suggest the right next step. Thank you for your understanding.