How can auto-responders cause email loops?

Auto-responder loops are common and preventable:

Classic scenario:

Person A has vacation auto-reply. Person B also has vacation auto-reply. A's reply triggers B's reply. B's reply triggers A's reply. Loop continues until detected or rate limited.

Other auto-responder risks:

Auto-acknowledgment systems. Ticketing systems. Mailing list confirmations. Notification systems.

Prevention standards:

Precedence: bulk header: Signals auto-generated. Auto-Submitted: auto-replied: RFC 3834 standard. X-Auto-Response-Suppress: Microsoft extension. Do not reply to messages with these headers.

Best practices:

Only auto-respond once per sender per period. Check incoming headers before responding. Rate limit auto-responses. Never auto-respond to mailing lists.

Auto-responder loops are two robots endlessly greeting each other. Proper header checking stops the madness.