last logon time Users
Enable attribute Last logon time in get-msoluser to be able to know when a user enters the portal, currently only you can get Access Log, "last logon time", with PowerShell in Exchange Online.
This is critical to our organization because the lastlogontime in on-prem AD does not get updated when users authenticate with ADFS. And Office 365 is all we use ADFS for.
I have contacted Microsoft and was notified that this exchange mailbox statistic is not accurate.