How do bounces affect deliverability metrics?

Bounces directly impact deliverability through multiple mechanisms:

Sender reputation signals:

High bounce rates indicate poor list hygiene. ISPs interpret this as a sign of spammy or careless sending. Reputation scores decline accordingly.

ISP responses to high bounces:

Throttling: Slowing down message acceptance. Increased filtering: More messages sent to spam. Temporary blocking: Rejecting messages entirely. Permanent blocking: For severe or persistent issues.

Metric thresholds:

Hard bounce rates above 2% are concerning. Above 5% often triggers account review at ESPs. Above 10% typically results in suspension.

Long-term impact:

Bounce history factors into reputation for months. Recovery requires sustained good behavior. Prevention is far easier than recovery.

Bounces are warning signals. High rates tell ISPs you are not maintaining your list or not sending to real subscribers.