My intuition is that a company’s collection of email messages is a rich source of useful information, and people will pay for a service that gives them access to it. What could users do in practice though?

Discover experts. By analyzing each person’s sent messages, it’s possible to figure out some good tags to describe them. These would need to be approved and tweaked by the subject before being published, but then you’d have a deep company directory that anyone could query. So many times I’ve ended up reinventing the wheel because I didn’t know that somebody in another department had already tackled a particular problem.

Uncover expertise. Email is the most heavily used content-generation system, hands-down. There’s lots of valuable information in messages that never makes it to a wiki or internal blog. The trouble is, that information quickly vanishes, emails are ephemeral. Any mail that’s sent to an internally public mailing list should be automatically included on an intranet page that’s searchable by keyword, or by person or team. You should also have a button in Outlook that lets you publish any mail thread on that same page. Those published messages produce something very like a blog for each person, effortlessly.

Work together. People collaborate by emailing each other attachments. Rather than trying to change that, put in a tool that by default uploads the attachment to Sharepoint, accessible only by the email recipients, and rewrites the message so it links to that instead. You’ll need a safety-valve that allows people to override that if they really do need it as an attachment, but this method should retain most of the advantages of email collaboration (clear access control, ease-of-use) and add the collaboration benefits of change tracking and a single version of the file.