You can ask the user to uncheck the check button under right notification pane (where it says "send me activity e-mails"). Note though that this option works globally, that is the user won't receive any notifications at all from any workspace.
On the other hand we try to limit the number of emails sent to users if they're not active, that is if you upload 5 documents the sharee will receive only one notification until he logs in. After that if you upload another batch of documents again only one email will be sent until the next login, and so forth.