When requesting files (upload link), you have the option of being notified by e-mail of each upload. With a FREE account, this e-mail notification is enabled by default and cannot be disabled.
However, as a PLUS or PRO user you can enable and disable this in the settings for the transfer under “Notifications” > “Notification with every upload”, either when creating the transfer or afterwards.
You can also check whether files have already been uploaded in your account at any time by going to “Transfers” > “Requested” > Select transfer > “Files”.