According to the help files, I should supposedly save the attachment with a differently named extension, except it won't let me access it in order to save it. I would go with the new hypothesis that that instruction is meant for the sender, but that's stupid - how would the sender know what client the receiver is using? And anyway, it doesn't help me as I am not the sender.
Meanwhile, my initial help search turned up this piece of crap paternalistic bullshitty article on the subject, and now I want to kick things. I am annoyed to the point that, rather than fuck with my client until I figure out how to make it do what I want, I'm just having her send it to my gmail account.
Outlook has its good features, but I totally understand why some people hate it, and I hate it part time myself. I'm just too tech-lazy to look for alternatives.