Sorry, I was unclear. You can't block people on either the free or paid plans, because you're supposed to ask your HR department to ask people to behave, and if you don't have an HR department you're 100% not their target audience. I've complained about this to Slack multiple times before, see their responses about how as a tool built for work they can't implement a block feature: https://twitter.com/geofft/status/767857284827475968 https://twitter.com/geofft/status/770000987016818688 https://twitter.com/geofft/status/818517767607517184 https://twitter.com/geofft/status/1017193464415576065