If you have storage expiry enabled, and you have enabled the Expiry Report button in Outlook, end users can click on the button and get a "live view" of what data is about to be expired from Enterprise Vault.
The way that this works is that the button in Outlook makes a call to searcho2k.asp, passing a parameter to indicate that you want to receive the Expiry Report (rather than the more normal "integrated search" web page). On the server side of things, the index for the users archive is queried for items which are about to expire (based on retention category etc) and then the results returned to the client. Remember that you can set expiry based on archived date or modified date (the default being archived date).
This is what the request looks like when it comes on to the Enterprise Vault Server :
2011-03-29 09:14:19 192.168.1.2 GET /EnterpriseVault/searcho2k.asp server=EXCH1&mbx=SMTP:pfg1@EV.Local&version=1000000000&vaultid=11437547DE43529439EC2BB99F41168421110000evsite&ep=1&outlook_redirect=1 80 EV\pfg1 192.168.1.189 200 0 0 1821 527 10140