What Is Hard Bounce?
A hard bounce is a permanent email delivery failure — the address is invalid, the domain does not exist, or the server has permanently rejected the message. Hard bounces should be removed from your list immediately, because repeatedly sending to them signals poor hygiene and harms reputation.
Hard bounces come back with permanent SMTP error codes (5xx) meaning "do not try again." Common causes are mistyped addresses, employees who have left a company, and fabricated addresses from purchased lists.
The critical rule: suppress hard-bounced addresses on the first bounce and never mail them again. Mailbox providers interpret repeated sends to known-dead addresses as spammer behavior, and it is also a strong indicator you are hitting spam traps.
Keeping hard bounces under roughly 2% of sends is essential. A spike usually means a stale or unverified list — validate addresses before your next campaign.
MailPilot keeps your warmup engagement flowing to real, valid mailboxes, and its placement and bounce monitoring help you catch list-quality problems before they escalate.
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