How do repeated soft bounces become hard bounces?

Soft bounces become hard bounces through persistent failure patterns:

The conversion process:

An address soft bounces on first send (mailbox full, for example). Subsequent sends continue to soft bounce. After multiple consecutive soft bounces over time, the ESP treats it as effectively permanent. The address is suppressed as a hard bounce.

Typical thresholds:

3-5 consecutive soft bounces. Over a period of 7-30 days. Varies by ESP and bounce type.

Why this makes sense:

A mailbox that has been full for weeks is effectively abandoned. Repeatedly trying is wasting resources. The recipient is not receiving or managing mail.

ESP implementation:

Track soft bounce history per address. Apply escalation rules. Convert to hard bounce or permanent suppression. Often configurable by sender.

Persistent temporary becomes permanent. An inbox that never clears is effectively dead.