At the moment MailRaider is a relatively barebones offering—it’s still in beta—but for basic needs, it should work well. The app can read Outlook emails and extract attachments, so it’s off to a good start. It’s not an email client, though, so don’t expect to send or receive any email; it’s just there to read whatever email isn’t yet in a Mac-friendly format.
MailRaider is freeware (donations are encouraged), Mac OS X only.
MailRaider [via Mac OS X Freeware]