Hi rm49640,
Mailing lists are a great way to make sure your customers are receiving updates about the products they buy or the services they're using through your business. I've got a few reports I can suggest for you to help you compile such a list in Excel.
Reports such as Sales by Item Detail or Sales by Class & Item Type could both be useful for you in this case. Running these reports will group your sales by products and details, allowing you to see all customers that have used purchase that item type. If you use classes to sort your transactions, the second report could be useful for seeing which customers are buying from which class as well. One of the options on the Sales by Item Detail report is to add a column to see the item descriptions as well.
Check out the Customize reports in QuickBooks Desktop article to learn more about the customization options and how to implement them. and play around to create a report that will help you create your list.
I hope that helps! I'll be here if you need anything else. :)
