I explored their web site a little bit and found no information about this alz format. It's probably proprietary, so I won't be able to add this format to BetterZip. But ALZip can also create zip files, so maybe your clients can zip files before sending them to you instead of alzipping.

Thanks for the quick reply; I will try again to convince them (already tried without success...). In the meanwhile I have just purchased a business license.

Great, thanks. Merry Christmas!