EDD Ban Emails
This is included in EDD core as of version 2.0+
Allows you to place emails in a banned list. These emails will not be allowed to make purchases.
Once activated, a new section will be added to Downloads > Tools where you can enter the banned emails. Email addresses should be entered one per line.
If a customer attempts to checkout with a banned email, they will receive a generic "interal" error that tells them to try again or contact support, but they will not be allowed to complete the purchase so long as they are using a banned email.