I see that MKeyes contacted the vendor and was told,

the corruption of the file occured during your transfer so it is on your end the problem

This is a typical example of bad, inept, callous, untrained tech support.  The "Blame the User" form of tech support. 

After all, if the vendor gets a payment and you don't get the product ... someone was stealing from you. 

As to a correction ... winZIP 9.0 (and above) have the ability to split a ZIP file into to allow eMail.  The RMP could use that program to split a large ZIP into sections of ... say, 1.4MBy and eMail each of those parts.  The purchaser could then extract those parts into a single folder and use winZIP to get the product.  BTW, at this point we don't know if such eMail messages would also become corrupted, do we? 

Another possibility would be for the RMP to copy the affected ZIP files to a notebook PC; take that PC to a reliable internet connection; upload the ZIP files to different ISP and notify the affected users aboout the alternate file locations. 

Of course, first they would have to recognize the need to be serious about this issue.  ... and spend a little money. 

Comments ... please. 

--
Martin