I go to Johns Hopkins University and they have a pretty effective way of dealing with the whole spam situation. Firstly, users can opt-in to the spam filtering system, which means that each user knows if they should expect emails to randomly disappear. Now, if they do opt-in, all "spam" is sent to an isolated quarantine inbox (as one might expect) by analyzing TO:, FROM:, Subject:, etc fields. The interesting part (which I think would solve your problem), is that if a user's spam inbox contains any messages, the spam daemon will send the user a digest email, containing a brief description about how it caught __ number of emails, etc. and will provide the subject headings for each email, along with a link to see the entire message. The user can then specify how often he/she wants these digests, which essentially guarantees that in a given period, the user will only have to consider spam emails once. Finally, the spam daemon automatically kills any emails left in the box after a certain amount of time.
This also has an added security benefit: emails classified as spam are never sent to the user (unless they explicitly request it), which means that if the message were to contain malicious attachments, unwanted images, etc, they are not at risk.
Anyway, just might be something you want to think about.