This document discusses the importance of email marketing and email list hygiene. It notes that email allows for engaging existing customers and donors anytime with tailored messages. However, email only works if the messages reach the inbox. It emphasizes the need to maintain clean email lists by knowing your audience, monitoring for inactivity, removing invalid addresses, using email change of address updates, and getting creative with re-engagement strategies. The overall message is that email is crucial for customer communication, but list attrition and invalid addresses can undermine its effectiveness if not properly managed.