Lena Dunham's Lenny Letter has 400,000 subscribers and an open rate of 65%

"This mix has helped Lenny Letter reach more than 400,000 subscribers, and the newsletter has a covetable 65 percent open rate. All content is also published to the Lenny Letter website (after a delay), and the site’s uniques topped 600,000 in February. While Lenny Letter doesn't have thorough demographic information on its readers yet, most are women between the ages of 18 and 34."
Source;  Nieman Lab, 2nd March 2016