A lead follow-up workflow can look healthy for days while nothing reaches anyone. The dashboard stays green, the API returns a message id, and the client finds out when a prospect complains. The three failure modes I see most: 1. "Accepted" is not "delivered" The send API answers with a success code or a message id. That only means the provider took the request. Delivery can still fail later: trial account limits, a dead webhook, a status code nobody is reading. If you only watch the send step, you miss weeks of undelivered follow-ups. 2. Silence looks like a quiet week A dead trigger or a broken webhook looks the same as a slow period. No errors fire. Volume just drops to zero. I treat "zero sends in a window where we normally send N" as a failure, same severity as a red error. 3. Timeouts that double-send, and skips you cannot see A timeout after the email already went out can make a retry fire a second copy. And a skip with no log looks broken to the client. Log the skips too. The daily check that catches this: one test message to my own number or inbox every morning, through the same path the client leads use. If that test does not land, I know before the client does. Second layer: alert when no status comes back within 10 minutes, and on failed or undelivered delivery callbacks. Thrown errors alone miss most of this. I also open-sourced the Claude Code skills I use for the rest of client work (scoping, quoting, outreach sequences). MIT, no email wall: https://github.com/CalebAnderson-Coder/ai-agency-os-starter Which silent failure have you actually been burned by on a live follow-up workflow?