Uh? Which mail server are you planning to use? Whatever it is, it has to handle the upload to the clients. You upload to the server, the server upload to the clients. Let's make it 1MB. Original transfer: 1MB uploaded by you to each client: 2MB. With mail server: 1MB to the mail server, 2 MB from the mail server to the clients. 3MB. You WASTE bandwith. Not counting the encapsulation on the new protocol, which is a lot. A LOT. Mails doesn't sent binary, except when encoded on text. And there's no mail server in the world that can handle such massive traffic.
you upload once, but you force the mail server to upload twice. Either you use someone's (ISP?) mail service, which is terribly wrong in every single way (see: webcache, only worse), or you create a dedicated server just for that, and given the amount of data, you could as well make it a pure client or an ftp server. Really, where are you going to get several barrebone servers with terabytes of bandwith and unlimited traffic?