The Reply-All That Wasn't: Agent Outbound Fan-Out Hazards
The user asked the agent to "let Karen know we're done." The agent called send_email with the recipient field set to karen-team@, the most plausible address its contact-lookup tool returned. The message — three paragraphs of internal-only project status, including a candid line about a customer's renewal risk — landed in forty inboxes. One of those inboxes belonged to the customer in question. The postmortem ran for two weeks.
There was no prompt injection. There was no model jailbreak. The tool worked exactly as specified. The contract the team wrote for send_email was "send a message to a recipient." The contract the world enforces is "broadcast to a group whose composition the sender did not audit." That gap — between what the tool is named and what the tool can actually do — is where most outbound agent incidents live.
Email is the obvious example, but the same hazard hides in every messaging tool an agent ever touches. The thirty years of muscle memory humans built for these channels did not transfer to the planner pattern-matching its way through a contact list.
