In the order form, you can set ModernBill to ban all free emails (such as yahoo and hotmail). If, however, you have specific email addresses you would like to ban, you can set this up here. For example, say you think yahoo email is ok, but you don't want anyone with a gmail account. You can set up a ban for gmail.com, rather than having to ban all free email addresses. Start by clicking on System -> Order Settings -> Show Bans. Here you will see a list of the emais that are already being banned by your system. You can edit these entries, make them inactive or active, and remove them if needed.