Preventing duplicate e-mail addresses

Hey there,

I have CF7TDB set up and it’s working great, however, I want it to be able to prevent users from submitting the form with the same e-mail address. Is there a way I can set it up to prevent it from allowing a duplicate e-mail address from one already in the database?

Thanks

http://ww.wp.xz.cn/extend/plugins/contact-form-7-to-database-extension/