Some months ago I tried to send a ZIP file containing a EXE file which is forbidden to be sent on Gmail. Gmail is extracting the ZIP file and will not send the email until it is removed. Some users have renamed the ZIP file to something like dummy.dat. The receipient has to reanme it back...
I tried to send this file as dummy_ZIP. If you get such email within Gmail the Internet Explorer will save it as dummy_ZIP.ZIP which is the correct file extension for ZIP files. SO, there is no need to change the filename back. I did not test if this is also working with standard email clients like Outlook.