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What Is a Bounce Rate (in Email)?
TL;DR
Bounce rate is the percentage of sent emails that fail to reach a recipient’s inbox — split into hard bounces (permanent failures, like a non-existent address) and soft bounces (temporary failures, like a full inbox) — and it’s one of the strongest signals mailbox providers use to judge sender reputation.
Hard bounces vs. soft bounces
A hard bounce is permanent: the email address doesn’t exist, the domain is invalid, or the server has permanently rejected mail to that address. Hard bounces should be removed from a list immediately and never retried.
A soft bounce is temporary: the recipient’s inbox is full, the receiving server is briefly down, or the message was too large. Soft bounces can resolve on their own, but an address that soft-bounces repeatedly over time should be treated similarly to a hard bounce.
Why bounce rate matters for deliverability
Mailbox providers read a high bounce rate as a sign that a sender isn’t maintaining or verifying their list — the same signal a spam trap or a scraped list would produce. Consistently high bounce rates damage sender reputation and can trigger volume throttling or outright blocks from a provider.
Most cold-email platforms and deliverability guidelines treat a bounce rate above roughly 2% as a warning sign, and rates approaching 5% or higher as an active deliverability problem requiring list cleanup.
