Every day, thousands of people make donations to humanitarian, political, environmental, and other causes, a large amount of which occur on the Internet. In our paper presented at CSCW'14, we describe a comprehensive large-scale data-driven study of donation behavior. We analyze a two-month anonymized email log from several perspectives motivated by past studies on charitable giving: demographics, user interest, external time-related factors and social network influence. We show that email captures the demographic peculiarities of different interest groups, for instance, predicting demographic distributions found in US 2012 Presidential Election exit polls. Furthermore, we find that people respond to major national events, as well as to solicitations with special promotions, and that social connections are the most important factor in predicting donation behavior.