How to copy old user’s mailbox to another user’s mailbox on Office 365 and Exchange Server using PowerShell
You will come across the issue with leavers mailboxes needing to be transferred to another users mailbox. If you are looking after on-site exchange, then the process is slightly shorter as you don’t need to connect to the remote Powershell.
To connect to O365 first run this PS command:
$Cred = Get-Credential
$s = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://ps.outlook.com/powershell -Credential $cred -Authentication Basic –AllowRedirection
PS command to transfer mailbox items:
Search-Mailbox -Identity “Old User” -TargetMailbox “Current User” -TargetFolder “Old-Mailbox” -LogLevel Full