"usually" is the key word there. A previous employer had a "learning" team that used their slack bot to send unblockable DMs to everyone in the company every time they released optional employee trainings. "Work like an NBA player!" The manager was verbally abusive to anyone who brought it up as an issue too.

They didn't program the bot very well though, because it had a separate employee->acct list from the org that you could modify to change who was messaged.