As discussed, you can perform a eDiscovery to search particular folder data from user’s missing folder then export the results in to a PST file like this:

Export eDiscovery Search Results to a PST File

Please refer to this page for more eDiscovery related information:

In-Place eDiscovery in Exchange 2016

https://technet.microsoft.com/en-us/library/dd298021(v=exchg.160).aspx

 

Export eDiscovery search results to a PST file

https://technet.microsoft.com/en-us/library/dn440164(v=exchg.160).aspx

 

to check the mailbox status of this user, you can do so by using Powershell commands:

· Run Windows PowerShell as Administrator.

· Set-ExecutionPolicy RemoteSigned

1. Run command $UserCredential = Get-Credential, press Enter, login the account.

· run command $Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://outlook.office365.com/powershell-liveid/ -Credential $UserCredential -Authentication Basic –AllowRedirection, press Ender

· run command Import-PSSession $Session, press enter

 

 

 

·         Run Get-MailboxFolderStatistics -Identity chris

· Then from the information presented, try to find the folder with the name of missing folder

 

Here are some more information that might be help:

 

Get-MailboxFolderStatistics

https://technet.microsoft.com/en-us/library/aa996762(v=exchg.160).aspx