How do MTAs manage bounce handling?
MTAs categorize bounces by response codes and messages. Hard bounces (5xx) indicate permanent failures: invalid addresses, non-existent domains. Soft bounces (4xx) indicate temporary issues: full mailboxes, server unavailability. Each requires different handling.
Hard bounce processing: immediately remove address from sending, log for analytics, potentially notify sender. Continued sending to hard bounces damages reputation. MTAs typically suppress hard bounced addresses automatically.
Soft bounce processing: queue for retry, track attempt count and age, escalate to **hard bounce** after threshold. Persistent soft bounces (same address failing for days) should eventually convert to suppression. Good MTAs provide detailed bounce categorization for analytics and list hygiene.
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