How can I prevent email loops in my system?

Loop prevention requires multiple safeguards:

Header-based prevention:

Set Auto-Submitted: auto-replied on auto-responses. Add Precedence: bulk to automated mail. Include X-Loop headers with unique identifier. Check these headers before responding.

Envelope handling:

Use null Return-Path (<>) for DSNs and auto-responses. Never send bounces about bounces. Verify envelope sender before generating DSN.

Detection mechanisms:

Track message IDs seen recently. Count responses to same address in time window. Monitor for rapid message accumulation. Implement circuit breakers.

Rate limiting:

One auto-response per sender per day. Limit DSN generation rate. Cap total automated responses per hour.

Configuration review:

Audit forwarding rules for cycles. Test auto-responders before deployment. Review mailing list configurations.

Loop prevention is defensive driving for email. Multiple safeguards catch what single measures miss.