The easiest way to do it is by uploading your email and subscriber list to Facebook, make a Custom Audience from them and then use this Custom Audience in your ad set level targeting when you create your retargeting campaign. You can even automate this process with Zapier or similar software that would export the list out of your email provider and upload it to Facebook. One of the most popular email software, Mailchimp even provides direct integration with Facebook so you don’t even have to setup the automation to work. If for some reasons, uploading the list to Facebook method doesn’t work for you or the match rate turns out to be terrible, you can also try to make a Lead or a CompleteRegistration Standard Event.