Hello Lauren,
Thank you for reaching out to the Microsoft Community and I'll be glad to assist you today.
I'm sorry you're experiencing this problem. I understand how important securing your account is to you.
It's good to know that you've secured your account with Microsoft Authenticator, making it difficult for unauthorized access. However, it can be concerning to receive frequent notifications on the authenticator.
1. Change your Microsoft Account Password:
If this is a personal account, please use the following link to reset the password: https://account.live.com/ResetPassword.aspx
2. Remove unused devices from your Microsoft account:
a. Go to https://account.microsoft.com/devices and sign in.
b. Remove unused devices from the lists.
3. Sign out everywhere:
a. Sign in to the Security page for your Microsoft account.
https://account.live.com/proofs/Manage
b. Scroll down and select Sign out everywhere.
(You will be signed out of browsers, apps and anywhere else your account is used to sign in, where possible, within 24 hours.)
- If you are still experiencing issues, and you still receive the unusual activity sign-in, Add an e-mail address as an alias to your Microsoft account.
"Outlook.com lets you have multiple aliases associated with a single account, and you can choose which email address you send email from. Creating alternate addresses to use on websites or apps that force you to register can help keep your personal email address out of the hands of marketers and hackers."
See "Add an email alias in Outlook.com" for reference:
https://support.microsoft.com/help/459b1989-356...
Keep your Microsoft account safe and secure -
https://support.microsoft.com/help/628538c2-700...
I hope this information helps. If you have any questions, please let me know and I will be happy to help you further.
Best regards,
Gunasekar N