Bounce >5% trips ISP throttling. Audit KL01 fires here.
At a glance
The percentage of sends that ISPs rejected or could not deliver. Computed as SUM(bounces) ÷ SUM(recipients) × 100 aggregated across every campaign in the period. Bounce rate is the single most important deliverability signal: above 5% Gmail and Yahoo start throttling the sender domain, and once throttled it takes weeks to recover.
Calculation
Calculated automatically from your Klaviyo data. See the At a glance summary above for what the metric tracks and the worked example below for a typical reading.Worked example
A skincare brand with a 145,000-subscriber list runs the following email campaigns over the 30-day window 14 Mar 26 to 12 Apr 26:- The headline 4.43% looks safe but the trend is dangerous. Below the 5% alert threshold by a hair. The two cleanup-style campaigns (Win-back tier 1, Re-engagement) are running at 11% and 13.5% individually, well above where Gmail and Yahoo start throttling. The blended figure is hiding two unhealthy sub-segments behind three healthy ones.
- Mother’s Day at 5.4% is a list-quality red flag, not a content problem. A tentpole campaign should bounce at 1-2%, similar to the regular promotional sends. 5.4% on a high-engagement segment usually means the merchant fired the campaign at the full list including dormant cleanup tiers, not a clean engaged segment.
- Win-back at 11% bouncing is normal but the strategy is wrong. Win-back campaigns inherently bounce more because they target less-engaged subscribers whose addresses degrade faster. This is fine in isolation, but combining a win-back send into the same 30-day window as promotional sends drags the blended bounce rate up and risks domain reputation. Segment win-backs to a separate sub-domain or sunset earlier.
- Hard vs soft bounce split is invisible at the API level. Klaviyo’s 2024-10-15 revision returns one combined integer. The merchant must drill into the Klaviyo dashboard per-campaign to see whether 11,070 bounces are mostly hard (kill those addresses) or soft (retry-able). Vortex IQ surfaces the rate; the dashboard surfaces the split.
- Above 5% triggers ISP throttling within 7-14 days. Gmail’s Postmaster Tools shows domain reputation degrading on the third or fourth send above the threshold. The fix is suppression of the worst-bouncing 5-10% of the list, not “send less”, merchants who pause sends entirely lose engagement signal which makes the next send bounce worse.
Sibling cards merchants should reference together
Bounce rate is a deliverability symptom, not a cause. Pair it with these:Reconciling against the vendor’s own dashboard
Where to look in Klaviyo: Klaviyo → Analytics → Deliverability for the headline bounce rate over time. Klaviyo’s own dashboard breaks this down per-campaign and per-ISP, this card sums it across all campaigns to a single account-level figure. The figures should match this card to within a few hundredths of a percent. Other Klaviyo views that look like the same number but aren’t:- Campaigns → individual campaign view → “Performance”: per-campaign bounce rate only. This card aggregates across all campaigns in the period.
- Lists & Segments → individual list → “Health”: list-level bounce rate, computed against the list’s most recent send. Different denominator.
- Reports → Custom Reports: can be configured to match this exact metric. Default reports differ.
- Account Settings → Sender Reputation: Klaviyo’s blended reputation score that combines bounce, spam, and engagement. Not the same as bounce rate alone.
Cross-connector reconciliation:
Bounce rate is a Klaviyo-internal metric. There is no commerce platform or analytics tool that surfaces a directly comparable figure. The closest cross-references are:
Known limitations / merchant FAQs
My bounce rate jumped from 1.5% to 6% overnight, what happened? Three usual causes, in order of likelihood: (a) you sent to a list segment you don’t normally use (a dormant cleanup tier, a re-engagement segment, a recently imported list); (b) you imported new subscribers without a confirmation flow, so untyped or fake addresses entered the list; (c) a B2B-heavy send hit a corporate domain that blocks bulk senders. Open the offending campaign in Klaviyo dashboard, sort campaigns by bounce rate to find the culprit, and suppress the worst-bouncing 5-10% before sending again. Is my bounce rate hard or soft? Klaviyo’s 2024-10-15 API revision returns a single combined integer. Vortex IQ shows the combined figure. To see the split, open the specific campaign in Klaviyo’s dashboard, the per-campaign performance view shows hard vs soft separately. Hard bounces (5xx SMTP errors) are permanent and Klaviyo auto-suppresses; soft bounces (4xx, mailbox full, temporary failure) retry and only suppress after several consecutive failures. Above what bounce rate do ISPs throttle? Gmail and Yahoo throttle above 5% sustained over multiple sends. Microsoft (Outlook, Hotmail) is stricter, around 3% triggers reputation degradation. Apple Mail rarely throttles purely on bounces. The 5% alert threshold here is a Gmail/Yahoo trigger; if your audience is heavily Outlook, watch for trouble at 3%. What should I do when bounce rate breaches 5%? Pause campaign sends to your full list immediately. Run a list cleanse: suppress everyone who bounced in the last 90 days, plus everyone with zero opens in the last 180 days. Then send a single low-volume re-engagement campaign to the cleaned list. Watch the rate over the next 2-3 sends, it should drop below 2%. If it doesn’t, investigate authentication (SPF, DKIM, DMARC) and consider warming a fresh subdomain. Does this card include flow bounces? No, this card aggregatescampaign-values-reports only. Flow bounces are tracked separately by Klaviyo and are not pulled here. For most merchants, campaigns are 80-90% of total send volume, so the campaign bounce rate is a reliable proxy for overall list health. If your account is flow-heavy (high abandoned-cart volume, high welcome-flow volume), the true account-wide bounce rate may differ. Open Klaviyo Account Settings → Deliverability for the blended figure.
Does this include SMS bounces?
No, this card is email-only. SMS bounces (carrier rejected, invalid number, opt-out) are tracked in Klaviyo’s SMS deliverability reports separately and are not pulled into this metric.
Why is my bounce rate higher than industry benchmarks?
Healthy DTC bounce rates run 1-2%. Above that, the usual suspects are: list age (older lists degrade), import sources (imports without double opt-in include typos, throwaway addresses, role-based aliases), industry vertical (B2B is 2-3× higher than B2C because corporate filters are stricter), send cadence (sending too rarely lets addresses go bad before they’re cleaned). A 4% bounce rate isn’t a crisis but it’s a sign the list needs attention before it gets worse.
My account uses a custom sending domain, does that affect bounce rate?
The bounce rate doesn’t change but the consequences do. With a custom subdomain (mail.yourstore.com), reputation damage is contained to that subdomain and doesn’t bleed into the main store domain’s email reputation. Without one, throttling on Klaviyo’s shared infrastructure can ripple into transactional email (order confirmations, shipping notifications) sent through the same domain. If you’re regularly above 3% bounce rate, set up a dedicated sending subdomain.
Why does my bounce rate spike on Mondays?
Mondays often see higher bounce rates because corporate “out of office” auto-replies that bounce back are batched up over the weekend. Pure consumer (Gmail, Apple, Hotmail) lists don’t show this pattern. If your list skews B2B and your Monday rate is consistently 2× the rest of the week, that’s why; it’s not a list-quality problem.