Using an email pop-up in my Shopify store to increase sales

Yes, an email popup is a good way to collect customers' email addresses so you can keep communicating with them even after they leave your store. The main principle behind using an email popup is to identify what might motivate your customers to subscribe to your mailing list - a special offer, downloading a guide, etc. - and to set up the popup to appear at the right moment.

There are dozens of Shopify apps for creating and customizing popups, so you should select one that fits your needs and budget. I would definitely look for an app that enables you to run split tests (aka as A/B tests) so you can try different copy, design, and timing in order to see when you get the best results.

Keep in mind that the email popup is just a way to build your email list, so you'll need to work on your email marketing as well once you get subscribers. You'd probably have to look for another app (if you haven't already) to run and manage your email marketing campaigns once you have email subscribers. Or you could use an app that does both.

One of the main features you should look for is integration between the popup app and your email marketing app so that your new email subscribers are automatically imported from the popup into your mailing list.