Shared mailboxes have Entra ID accounts. No one needs to sign into the accounts because Exchange Online manages connections using mailbox permissions. But it can happen that people do sign into shared mailboxes and if the accounts aren’t licensed, they don’t comply with Microsoft licensing requirements. As explained here, some PowerShell can check for potential licensing violations.

https://office365itpros.com/2024/08/26/shared-mailbox-signin/

​ 
Shared mailboxes have Entra ID accounts. No one needs to sign into the accounts because Exchange Online manages connections using mailbox permissions. But it can happen that people do sign into shared mailboxes and if the accounts aren’t licensed, they don’t comply with Microsoft licensing requirements. As explained here, some PowerShell can check for potential licensing violations.
 
https://office365itpros.com/2024/08/26/shared-mailbox-signin/  Read More

​