Whenever you move a mailbox in Exchange Server the LastLoggedOnUserAccount attribute of the mailbox is changed to the user running the mailbox move. This is confusing since that user does not need permission to log on to the mailbox to perform the move.

It can also present a problem if you are trying to figure out which users have yet to log on to their mailboxes after moving them between servers. Let’s say you run this command:

Get-MailboxStatistics | where { $_.LastLogonTime -eq $null }

This would show you which users have never logged on to their mailboxes. Whichever servers they originally were located on cannot be removed before they have logged on at least once and been redirected to their new mailbox servers. Unfortunately, since the user performing the mailbox move is added to the LastLoggedOnUserAccount this command will probably return no users.