He said it has a .exe extension. It's possible that the originator did
his a "favor" by doing a Save for Service Provider, then zipping the
folder into a self-extracting archive (an option in WinZip, for
example). This would be less than helpful, I presume, on a Mac. But it
would account for the extension.
The easiest solution would be to have the person resend the zip file
without the self-extraction feature. If that person is either
unavailable or clueless, the OP could send me the file and I could
extract it and rezip it. In fact, I think WinRAR will produce a StuffIt
file, although I haven't tried that option yet.