Email can deliver mobilization messages at considerably lower cost than direct mail. While voters’ email addresses are readily available, experimental work from 2007 to 2012 suggests that email mobilization is ineffective in most contexts. Here, we use public data to reexamine the effectiveness of email mobilization in the 2016 Florida general election. Unsolicited emails sent from a university professor and designed to increase turnout had the opposite effect: emails slightly demobilizing voters. While the overall decrease in turnout amounted to less than 1 percent of the margin of victory in the presidential race in the state, the demobilizing effect was particularly pronounced among minority voters. Compared to voters from the same group who were assigned to control, black voters assigned to receive emails were 2.2 percentage points less likely to turn out, and Latino voters were 1.0 percentage point less likely to turn out. These findings encourage both campaigns and researchers to think critically about the use and study of massive impersonal mobilization methods.