On your exchange 2007 server open Internet Explorer and enter the URL
<servername> will be the name or IP address of your server and <UserName> is the user name of the user who’s mail you want to look at.
When prompted for logon details, using the administrator account should give you access to any users mailbox.
From their you can see their sent items. You can also view the smtp log but that is a little cryptic and takes some searching.