Turn off Drop-Off Link Access by Firm

Our firm does not use SS Exchange, therefore we do not want our clients to have access to the Drop-Off option in the Portal. Currently we have to turn that off client by client. I currently have over 950 clients using the Portal, just from the ability to create it from the email last year. I don't have time to touch 950 clients to turn this off. PLEASE give us the option to turn it off in the Firm settings.