/ Glossary — Reputation & Bounces
What is a hard bounce?
A permanent delivery failure — the address doesn't exist or can't receive mail, and retrying won't help. Here's what causes it, why it hurts your reputation, and how to handle it.
/ Definition
A hard bounce is a permanent email delivery failure. It happens when a message can't be delivered for a reason that won't change on retry — most commonly because the recipient address doesn't exist, the domain isn't real, or the receiving server has permanently rejected the mail. Unlike a soft bounce, which is temporary, a hard bounce is final: the address should be removed from your list and never mailed again.
Hard bounces matter far beyond the single failed message. Mailbox providers watch your bounce rate as a signal of how well you maintain your list, and a high rate of permanent failures tells them you're mailing addresses you shouldn't — a hallmark of poor list hygiene that damages your sender reputation and drags down delivery to your valid recipients too.
/ In practice
What causes a hard bounce?
The most common cause is a simple typo or an address that was never valid in the first place — someone entered "gmial.com," or a fake address was submitted to a form. Others include an address that was once valid but has since been deleted, a domain that no longer exists, or a receiving server configured to permanently reject mail from your IP or domain. In every case the defining feature is permanence: the receiving side is telling you, unambiguously, that this address will never accept your mail.
How should you handle them?
The rule is simple and non-negotiable: suppress a hard-bounced address immediately and permanently, so it's never mailed again. Any competent sending platform does this automatically by adding the address to a suppression list. The deeper fix is prevention — validating addresses at signup, using double opt-in, and never importing unverified purchased lists, which are the single biggest source of hard bounces and the fastest way to damage a sending reputation. Watching your bounce rate over time is part of healthy deliverability monitoring.
/ Related terms
Bounces are a symptom. Clean sending is the cure.
A low bounce rate comes from list hygiene, validation, and infrastructure that suppresses failures automatically — all of which we operate. Bring us your sending and we'll keep your reputation clean.
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