What Counts as a High Bounce Rate?

A bounce is an email that could not be delivered. As a rough guide, aim to keep your hard bounce rate under 2 percent, and ideally close to zero. If a campaign bounces well above that, mailbox providers take it as a signal that your list quality is poor, and your inbox placement suffers.

Why It Matters

Mailbox providers judge your sender reputation partly on how often you try to reach addresses that do not exist. A high bounce rate tells them you are not maintaining your list, so they are more likely to route your future emails to spam, even for your valid subscribers. Bounces also waste send volume and skew your reporting.

Common Causes

• Fake or mistyped addresses from forms, pop-ups, and lead ads.
• Spam and bot signups that flood your list with junk addresses.
• Old, stale contacts that have since been deactivated.
• Importing an unverified list from another platform.
• Buying or scraping lists, which is both risky and against most policies.
• No validation step between signup and your send-eligible segments.

How to Fix It Now

If your bounce rate is already high, work through these steps:

• Pause large campaigns until the list is cleaned, so you stop adding bounces to your record.
• Verify your existing list with a validation tool and suppress the addresses that fail.
• Suppress contacts that have already hard bounced so you never email them again.
• Remove or re-permission long-inactive contacts who have not engaged in months.
• Confirm your authentication (SPF, DKIM, and DMARC) is set up correctly.

How to Prevent It Going Forward

Cleaning once helps, but bounces creep back in as new contacts sign up. To keep your bounce rate low for good, validate contacts as they enter your list rather than only cleaning after the damage is done. Use confirmed opt-in where you can, and keep an eye on engagement so you can sunset contacts who stop opening.

Where Mail Ward Fits

Mail Ward validates each contact the moment it enters a Klaviyo flow and suppresses undeliverable and risky addresses automatically, based on your preferences. Because it works at the point of signup, bad addresses never reach your send-eligible segments, so your bounce rate stays low without repeated manual cleanups. For a wider view of your options, see our guide to the best email validation apps for Klaviyo.

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