ZeroBounce.net takes security of your data seriously. When you download a file a password will be generated and email to you to access that file. The reason why we do this, is to add an extra layer of security. If someone was to comprise your account, they wouldn't have access to your data without that password.
The password you receive in email only applies the the file you downloaded. If you download a file a second time, you will be send a new password to access that file.