You can get an email list of QuickBooks users from several sources. You can search online for data providers that specialize in business and accounting software users. You can also check platforms that offer B2B email lists. You can find websites and forums where QuickBooks users gather and offer opt-in forms to build your list. You can consider using social media groups or communities related to QuickBooks. You can purchase targeted email lists from providers who focus on accounting software users. You must ensure the list is accurate and complies with privacy regulations before using it.