This is impossible. IF I am on an IE7 session, sign on to my comcast account and send email.....how does IT see my email?? They can't. (I use Windowwasher every day for cookies and tmp files)
Windowwasher will clear your PC, but it's safe to assume everything that goes out on the network is monitored and logged.
Like I said in an earlier post...typically the IT Dept (or at least specific people within the Dept) has access to all that info, we just don't care. Unless someone (for instance, your supervisor wondering about your performance) asks us to pay attention.
No, it's not impossible. Unless you're connected to the web server with an SSL connection, the information you've typed into the web mail client is transfered to the web server in clear text form. And I believe that most IM clients also send their data in clear text as well.
Mark