Overview

An email "bounce" happens when a recipient's mail server rejects or fails to deliver your message. High bounce rates hurt sender reputation and reduce inbox placement for future campaigns. The goal is simple: prevent bad addresses from being mailed and quickly suppress problematic ones.

Two Bounce Types

Hard = permanent failure. Soft = temporary issue.

Hard Bounces

Hard bounces are permanent failures. Typical causes include non-existent addresses, invalid or inactive domains, and firm rejections by the recipient server. Suppress these addresses right away so they cannot be mailed again.

• Address doesn't exist (typos, fake signups).
• Domain is invalid or misconfigured.
• Server rejects the address as unknown.

Soft Bounces

Soft bounces are temporary. They may clear on a later attempt. Common reasons include a full inbox, a momentary server outage, or transient policy limits. If the same address soft bounces repeatedly (for example, seven consecutive attempts), suppress it.

• Mailbox full or temporarily unavailable.
• Receiving server is down or overloaded.
• Temporary policy or configuration constraints.

Common Reasons Emails Bounce

• Content: Message resembles spam or malicious patterns.
• Message length/size: Exceeds provider limits.
• Frequency or volume too high: Spikes can be throttled or rejected.
• Invalid address: Typos, fake signups, or closed mailboxes.
• Invalid sender address: Misspelled or non-existent from address.
• Reputation: Poor domain or IP reputation triggers blocks.
• Mailbox unavailable: Full inbox, auto-reply, or server error.
• Technical: DNS/authentication problems such as SPF, DKIM, or DMARC failures.
• Unclassified: Ambiguous or generic rejection response.

Viewing and Suppressing Bounces in Klaviyo

In Klaviyo, hard-bounced addresses are automatically suppressed. Soft bounces are retried; repeated soft bounces over time should be suppressed to protect reputation. Use engagement segments and suppression lists before broad campaigns.

What to Review

• Recent campaigns: bounce rates by ISP and segment
• Affected profiles: pattern of hard vs. soft bounces
• Authentication results: SPF/DKIM/DMARC pass rates
• Complaint and unsubscribe trends

Suppression Rules

• Immediately suppress hard bounces
• Suppress addresses with repeated soft bounces
• Quarantine unknown addresses until verified
• Exclude risky cohorts from large sends

Where Our App Fits

Our app prevents bounces from harming your reputation by acting before an email is sent. You can set preferences to automatically suppress addresses that are invalid, undeliverable, or repeatedly problematic. This reduces wasted volume and protects inbox placement.

Statuses We Apply to Profiles

Prevention Playbook

• Use confirmed opt-in and validate inputs to reduce typos.
• Import only cleaned, recent lists; quarantine stale contacts.
• Authenticate your domain (SPF, DKIM) and enforce DMARC.
• Send predictably; avoid sudden volume spikes.
• Monitor bounce and complaint rates by ISP and segment.
• Auto-suppress hard bounces and repeated soft bounces.
• Use our app's statuses and events to target healthy segments first.

FAQ