My Office 365 tenant was recently upgraded to the “Wave 15” version of the service, meaning that my email is now hosted on Exchange 2013, rather than 2010 (Microsoft has provided an article that helps users to understand which version of the service they are on).
Unfortunately, since the upgrade, an awful lot of my legitimate email is getting trapped as junk. After moving it back to the Inbox, I noticed that one of the items displayed a message about retention policies, highlighting that it would expire in 30 days.
I don’t use retention policies (with gigabytes of empty space in my mailbox I don’t need to), so I thought this was a little strange, until I realised that this was a side effect of having been previously flagged as junk, where there is a retention policy set to remove mail after a month. I then found that the Managed Folder Assistant (which applies the retention policies) only runs every 7 days on Exchange Online but can be forced in PowerShell.
Sure enough, once I’d eventually managed to connect to Office 365 in PowerShell and run the
Start-ManagedFolderAssistant -Identity mailboxalias command, the email was no longer flagged for expiry.
There’s more information on setting up and managing retention policies in Exchange Online with Windows PowerShell on the Outlook.com help pages.