I routinely email zipped binaries to willing beta testers, have not had a problem yet.
With windows users, its best to tell them to unzip (happens automatically in the file manager) AND then drag the binary onto, eg, their desktop. That is, don't try to run it from within the zip file.
Some corporate email systems will scan attached zip files looking for (potentially nasty) binaries inside and block them just in case. And who can blame them ?
Davo