It looks like the good folks at Microsoft have updated the output of the Get-MailboxStatistics cmdlet with few additional properties. Here’s the full list:
LastEmailTime : 01/02/2019 15:17:05 LastContactsTime : 13/09/2018 18:55:35 LastCalendarTime : 25/01/2019 18:48:09 LastTasksTime : 21/01/2019 17:13:13 LastFileTime : 01/02/2019 21:55:48 LastProfileTime : LastInteractionTime : 01/02/2019 15:17:05 LastUserAccessTime : LastUserActionTime : 01/02/2019 15:17:05 LastUserActionUpdateTime : 02/02/2019 01:52:04
Since there is no mention in the documentation for any of there, we can make some educated guesses as to what each property represents. For example, the LastTasksTime seems to correspond to the date/time at which I last updated a task item in my mailbox, and in fact seems to be correct. On the other hand, properties such LastEmailTime or LastActionTime don’t seem to correspond to the actual time such operations were performed. And since they all have a similar value, we can guess that all of them are being updated by some background process on a regular schedule, which seems to introduce few days delay.
And that’s pretty much all I know about them at this time. I’ve probed Microsoft for more details, and should they share them or publish an article on the changes, I will make sure to circle back to this. It’s also worth noting that none of these properties seem to be available on-premises, at least not on Exchange 2019 RTM.