Outlook not receiving emails is a common issue. Before assuming it’s hacked, understand that it can happen for many reasons, such as emails being hidden, blocked, or stopped syncing.
Therefore, if you find out about this problem, give yourself five minutes to follow the steps given below:
Look in the Other tab, as emails sometimes land there. Also, check the Junk Email folder.
Make sure Work Offline isn’t enabled by checking the bottom-left corner of the Outlook window. If it’s enabled, Outlook has stopped connecting with the server.
Search for the sender across all folders using “from:sender@email.com”, not just Inbox.
Check whether the mailbox storage is full.
Ensure that you’re not signed out. If there is a red exclamation mark or “Disconnected” in the status, you won’t receive new emails until the issue is fixed.
Sometimes, the mail never came into your inbx in a form you could read. And the reasons include:
Your mailbox is full
A Microsoft 365 service outage
Your account is on a security hold
Other times, it could be due to a connection failure between your device and the server, not the delivery. If you have an antivirus installed on your desktop, it may also interfere with the email.
Source: Outlook Not Receiving Emails