[Belfaborac]

I would think this is a problem originating with the sender, considering it happens with both ePUBs and zips. Ask someone else to send you an ePUB and a zip and see if the same thing happens then. If not, the sender is the one with the problem; if the problem persists, you're the problem (well, your Outloook or your PC, or something).

I use Outlook too by the way and have never seen anything of the kind you describe.