What is an email loop?

An email loop is a message cycle that repeats indefinitely:

How loops form:

Message triggers automatic response. Response triggers another automatic response. Cycle continues without human intervention. Can generate thousands of messages quickly.

Common loop scenarios:

Auto-responder to auto-responder: Two vacation messages replying to each other. Bounce to bounce: DSN triggers DSN. Forward chains: Circular forwarding rules. Mailing list reflection: Message returns to list.

Damage potential:

Server resource exhaustion. Mailbox flooding. Bandwidth consumption. Potential blocklisting.

Detection:

Rapid message volume increase. Same headers repeating. Loop detection headers present.

Email loops are storms at sea. Once started, they can overwhelm everything in their path.