Managing personal Outlook.com account settings, security, and privacy
Hi Susan,
Thank you for posting in Microsoft Community.
We are sorry to hear that your account was hacked, and we are glad that you were able to recover it.
The hacker may have added your email to his/her an email application which is why you are receiving an attempt to sync the mailbox. However, the good news is you were able to secure the account and change the password. Due to this, the log in on the mail app on the hacker has expired which is why the syncing is failing.
The best thing you can do is to make sure that the security information on your account is always updated, accessible and safe from anyone since it is the most important part of the security of your account. The only way to regain access to your account is if they are able to hack and obtain access to the security information you have set up.
You can also visit this link for other tips you can do to keep your account more secure: How to help keep your Microsoft account safe and secure - Microsoft Support
Thank you very much for understanding and we hope this helps.
Best regards,
Ben Clement G