I didn't manage to find a public ActiveX interface for Outlook Express, but I did find one for Outlook, and a few quick tweaks managed to get a message in the outbox. For some reason it wasn't sent (maybe I didn't have a user set up properly), but you can try playing with it to see.
Another option would be to use the built in SMTP VIs (unless you need POP3).
___________________
Try to take over the world!