My outlook account notices some unusual IMAP Login from Microsoft

Dear

Welcome to Microsoft Community.

Here you see that when you check your account messages you see that Outlook has an IMAP mailbox status with a sync failure, and you need to confirm the specifics of IMAP.

IMAP is a method of accessing email that is manually selected when the mailbox is added to Outlook, IMAP allows you to access your email from any device, no matter where you are. When you use IMAP to read email, you are not actually downloading or storing it on your computer; you are reading it from an email service. So you can check your email from different devices anywhere in the world: your mobile phone, your computer, a friend's computer.

You can refer to the link:What are IMAP and POP? - Microsoft Support

In the case of your complaint about seeing off-site messages in your mailbox, it is possible that your mailbox account has been compromised due to, for example, a hacker attack on your account.

Since Microsoft has no control over the activities of hackers, we may take steps to protect your account and make it more difficult to hack.

To help resolve this issue, I recommend that you perform the following steps.

1. Check your recent activity page. This shows when and where you have used your Microsoft account in the last 30 days. You can expand any activity listed to see location details and find out how the account was accessed, using a web browser, phone or other method.

If you only see a Recent activity section on the page, you don't need to confirm any activity. What the activity page is:What is the Recent activity page? - Microsoft Support

2. Change your password immediately: This is the first and most important step to take. You should change your password to a strong, unique password that you haven't used before. Make sure you use a combination of letters, numbers and symbols to make it harder to guess:Reset a forgotten Microsoft account password - Microsoft Support

3. Enable two-factor authentication: This is an additional layer of security that requires you to enter a code sent to your phone or email before you can access your account. This will help prevent unauthorized access to your account in the future:How to use two-step verification with your Microsoft account - Microsoft Support

4. Check your account settings: make sure that your account settings have not been changed by the hacker. Check your settings, filters and email forwarding rules to make sure they are configured correctly.

5. Scan your computer for malware: It is possible that the hacker gained access to your account through malware on your computer. Run a full scan of your computer using a reputable antivirus program to check for malware.

Feel free to post back if you need further assistance.  

Best Regards, 

Chris.S-MSFT | Microsoft Community Support Specialist