Hard bounce
A permanent delivery failure.
A hard bounce means the recipient address or domain cannot receive the message permanently. Common causes include nonexistent addresses, invalid domains, or recipient servers rejecting the address. Hard-bounced addresses should be suppressed quickly.
reading this as growth and lifecycle teams
Growth work lives or dies on targeting and measurement. What matters is whether behavioral triggers can be built without engineering time, whether the event stream supports attribution past the open, and whether deliverability holds when broadcast volume shares a reputation with product email.
Applied to hard bounce, that means weighing scheduling, event stream, deliverability, and operating track record ahead of the rest, against behavior-triggered journeys, broadcasts, and winback campaigns measured on revenue.