You can use the Exchange Management Console to view who last logged on to a mailbox, the last logon date and time, the mailbox size, and the message count by completing these steps:
1. Expand the Recipient Configuration node and then select the Mailbox node.
2. Double-click the mailbox with which you want to work.
3. On the General tab, the Last Logged On By text box shows who last logged on to the mailbox, and the Modified entry shows the date and time the mailbox was last modified.
4. On the General tab, the Total Items and Size (KB) areas show the number of messages in the mailbox and the current mailbox size in kilobytes, respec¬tively.
If you want to view similar information for all mailboxes on a server, the easiest way is to use the Get-MailboxStatistics cmdlet. Here are some examples of using this cmdlet.
Get-MailboxStatistics -Server ‘corpsvr127’
Get-MailboxStatistics -Database ‘Engineering Primary’
Get-MailboxStatistics –Identity ‘cpandl\williams’