Hi,

I would recommend you to make copy of existing getfile page (~\CMSPages\GetFile.aspx.cs). You can place BizForm web part/control on this page and before letting user to download the file, he/she will need to post e-mail address. The information will be stored in the database and you can eventually store some information into cookie, so the user doesn’t need to submit the e-mail address every time he/she will try to download the file. I hope this will help you.

Best Regards,
Miroslav Remias.