Hi there, 

Sometimes it's necessary to be able to export your customer data out of QuickBooks. Rest assured, I'll be happy to share more info and make sure you're on the right path. QuickBooks offers the tools and resources you need in order to manage your accounting with peace of mind. 

Since there isn't a direct way to export just the customer emails. I encourage you to check out this article here that shows you how to export customer data via Excel. This exports the majority of the customer data, however, you'll have the flexibility to gather just the email info in Excel after you've exported out of QuickBooks. 

You're more than welcome to ask other questions in the comments below. I'm here to help you achieve your QuickBooks goals.