How do ISPs interpret repeated invalid addresses?

ISPs view repeated invalid address sends negatively:

What it signals:

Sender is not managing bounces. List may be purchased or scraped. Addresses were never validated. Careless or malicious sending practices.

ISP interpretation escalation:

First occurrence: Noted but tolerated. Repeated to same address: Strong negative signal. Pattern across addresses: Systemic problem flagged.

Reputation consequences:

Each repeat attempt counts against you. Signals multiply the damage. Indicates you ignore feedback.

Why it matters:

Legitimate senders suppress bounced addresses. Spammers often do not bother. Repeated attempts are a spam indicator.

Prevention:

Suppress hard bounces immediately. Process bounces in real-time. Never retry permanently failed addresses.

Sending to known-bad addresses is willful negligence. ISPs treat it accordingly.