When should I stop retrying and suppress the address?

Stop retrying when evidence suggests permanent failure:

Time-based triggers:

Retry window expired (48-72 hours). All scheduled retries exhausted. No successful delivery in extended period.

Error-based triggers:

Error upgrades from 4xx to 5xx. Final retry returns permanent code. Server explicitly indicates "do not retry."

Pattern-based triggers:

Same soft bounce across multiple campaigns. Consecutive soft bounces over weeks. Address never successfully delivered.

Suppression decision:

Single campaign failure: May not suppress immediately. Multiple campaign failures: Strong candidate for suppression. Consistent pattern: Suppress to protect reputation.

Recording the decision:

Log reason for suppression. Preserve bounce history. Enable review and potential unsuppression.

Suppression is admission of defeat. Stop retrying when evidence says the address is unreachable.