Summary: In this study, we examine how a firm’s decision to post on social media affects the propensity of its followers to (1) purchase its products and (2) unfollow the firm. Using a unique dataset from a large fashion retailer which frequently sends mass non-customized information-only posts on social media (i.e., non-coupons), findings indicate that such posts increase short-term purchases by 6%. However, these posts also increase followers’ propensity to unfollow the firm by 280%, significantly reducing long-term sales. Strikingly, this punitive effect of social media posting appears to manifest under very specific circumstances. Results indicate that these changes in unfollowing and long-term sales are larger if posts are sent in more crowded cities or during commuting hours (suggesting that the stress formed by personal crowding and the follower’s environment may play a key role in followers’ reactions to social media postings). These results underscore the potential downsides of sending blanket, non-customized, messages to followers, notably during times of intense psychological stress, as well as avenues to avoid such pitfalls. Posted online August 23, 2020