How do high bounce rates affect sender reputation?

High bounce rates directly damage sender reputation:

What ISPs conclude:

You are sending to invalid addresses. List quality is poor. Acquisition practices may be questionable. You are not maintaining your list.

Reputation impacts:

Immediate: Throttling and increased deferrals. Short-term: More messages filtered to spam. Long-term: Potential blocking and blocklisting.

Threshold concerns:

Hard bounce rates above 2%: Concerning. Above 5%: Serious reputation damage. Above 10%: May trigger ESP suspension.

Recovery difficulty:

Reputation damage accumulates. Takes sustained good behavior to recover. Prevention far easier than remediation.

Bounce rates are a report card on list quality. High rates tell ISPs you are not a careful sender.