Intro and estimate sent to provided email
A word of caution adding these things are not a panacea,if the core issue is lack of engagement or low conversions, slashes.co has a very clean design such that extra noise needs to carefully weighed.
Newsletters ,because of backend email service, are typically handled through apps b: https://apps.shopify.com/search/query?q=popup
"popups" need to handled with care to not alienate the target audience causing more damage than they're intended to fix.