Not to be difficult, but - Open-AudIT's primary goal is to tell you the configuration of the devices on your network - not how they are used (by users).
Your best bet would be to use a web proxy for the web traffic (I have used Squid in combination with a MySQL DB and some PHP to generate reports), and your mail server should be able to provide the Sent Emails from everyone (have it copy any sent emails to a seperate account).
Another product to check out may be Splunk. Don't know if it can do these particular logs, but might be worth checking out...
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