I save landscape reports in snapshot all the time. The only thing I have set is FILE+Page Setup+Landscape in the normal Page Setup screen.
How are you generating the snapshot file? Using FILE+SEND?
If you simply go FILE+EXPORT, change the type to Snapshot, and just save the file, does it come out ok? I just noticed on the FILE+EXPORT screen, a greyed-out check box to the right of where you pick the file type (Snapshot) that says "SAVE FORMATTED". Do you have that? I've never done anything to set that in any way.
Anyhow, to test this, simply save it in snapshot (vs. emailing) and see if it's landscape. tell me how it goes.