Engineering Guardrails to Prevent Auto-Reply AI Agents from Infinite Loops
kumard3 · reddit · 2026-08-10
When building AI agents for auto-replying to inbound emails, a critical and easily missed failure mode is two automated systems triggering each other in an infinite loop (e.g., endlessly replying to a vacation responder).
The author shares specific engineering guardrails to prevent this:
- Header Checks: Inspect auto-submitted and precedence headers (RFC 3834) before replying.
- Sender Filtering: Detect and avoid replying to no-reply senders.
- Caps & Self-Recognition: Limit replies per thread and stamp outbound emails with a marker header so the agent recognizes its own prior replies.
- Human-in-the-loop: Use a draft-first mode to queue replies for human approval, and trigger escalatetohuman via webhook when the agent is unsure.
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