Back in the days before ransomware and RATs and APTs and ubiquitous cloud-hosted corporate email, when viruses were accidentally introduced rather than spear-phished, state/criminal-gang-sponsored existential threats to a company, I had the idea (without the ability to manifest it) of a virus that would infect an MS Exchange instance and set everyone's Out of Office on and all incoming email to be forwarded to every other mailbox in the company.

Not sure if it is or was feasible, but I still like the simplicity of an automation-stack doing the really hard work of exponential amplification.