Hard + soft bounces / sends. Above 5% Mailchimp will throttle and ISPs will start blocking. Audit MC-DEL-001 fires.
At a glance
The percentage of sends that ISPs rejected or could not deliver. Computed as SUM(hard_bounces + soft_bounces) ÷ SUM(emails_sent) × 100 aggregated across every campaign and Customer Journey email in the period. Above 5% Mailchimp itself will throttle the account, and Gmail / Yahoo will start de-prioritising the sender domain. Audit MC-DEL-001 fires here. Unlike Klaviyo’s combined bounce figure, Mailchimp returns hard and soft bounces separately, so per-campaign drilldowns can show the split.
Calculation
Calculated automatically from your Mailchimp 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 B2B newsletter publisher running an industry-news email on Mailchimp Standard, single audience of 18,400 subscribers. Window 03 Apr 26 to 02 May 26.
Five observations:
- The headline 2.50% is healthy but the re-engagement campaign is a red flag at 16.7%. It’s hiding behind four healthy weekly sends. A re-engagement campaign bouncing >15% means the dormant tier is mostly dead addresses, the sensible move is to stop re-engagement and move dormant addresses to “cleaned” rather than continue contaminating sender reputation.
- Hard bounces are 65% of total here, more than typical. A healthy steady-state ratio is roughly 50/50 hard vs soft. 65% hard skews mean the underlying list quality is degrading, addresses are going stale faster than they’re being added. B2B lists do this faster than consumer (people change jobs, corporate domains decommission emails) so monitor the trend, not the absolute split.
- Mailchimp will auto-suppress 1,258 addresses from this re-engagement send. The “cleaned” count in Audience Size will jump by ~1,200 in the next read, which is the system protecting deliverability. Don’t manually re-add cleaned addresses; that’s a Mailchimp Compliance violation.
- At 2.50% the merchant is in the safe zone but watch the trajectory. Gmail throttles on sustained 5%+ over multiple sends. The re-engagement campaign single-handedly added 0.97 pp to the blended rate. Two more re-engagement attempts at this volume would push the 30D rate over 4%, dangerously close to throttling.
- B2B bounce profiles run higher than B2C. Corporate spam filters are stricter, addresses change with job changes, and out-of-office auto-replies sometimes register as soft bounces. A 2-3% steady-state for B2B is normal where consumer DTC would expect 1-2%. Don’t apply consumer benchmarks to B2B without adjustment.
Sibling cards merchants should reference together
Bounce rate is a deliverability symptom. Pair with these:Reconciling against the vendor’s own dashboard
Where to look in Mailchimp’s own dashboard: Mailchimp → Campaigns → Reports for per-campaign bounce rate, with hard/soft split visible on each campaign’s individual Performance tab. Mailchimp → Audience → Audience Health shows audience-level bounce trends. This card sums bounces and sends across every campaign + Customer Journey email in the period. Figures should match within ±0.05 pp. Other Mailchimp views that look like the same number but aren’t:- Account → Sender Reputation: Mailchimp’s blended reputation tile combines bounces, complaints, and engagement. Not the same as bounce rate alone.
- Audience → Audience Health: per-audience health score. Shows directionally but uses a different denominator window.
- Reports → Comparative Reports: ad-hoc set selection. Defaults differ.
Cross-connector reconciliation:
Bounce rate is a Mailchimp-internal deliverability metric. Closest cross-references:
Known limitations / merchant FAQs
My bounce rate jumped from 1.5% to 6% overnight, what happened? Three usual causes, in order: (a) a new bulk import without confirmation, freshly imported lists routinely bounce 8-15% on first send because addresses have aged, gone stale, or were typo’d; (b) a re-engagement send to dormant subscribers, dormant tiers always bounce hard; (c) sudden domain-reputation crisis (rare, usually only after a deliverability blunder upstream). Open the offending campaign in Mailchimp Reports, identify the source, and stop sending to that segment until cleansed. Are my hard and soft bounces broken out separately? Yes, on Mailchimp’s per-campaign Reports view. Mailchimp’s API returnsbounces.hard_bounces and bounces.soft_bounces as separate fields. This card sums them (the engineering decision matches the alert threshold convention), but to drill into one-or-the-other, click through to the campaign’s Mailchimp report. Klaviyo, by contrast, returns one combined integer; Mailchimp gives you the split if you want it.
Will Mailchimp suspend my account if I cross 5%?
Not immediately. Mailchimp issues a “list cleanse” notice via email, asking you to remove dormant subscribers within 7-14 days. Continued breach can lead to a temporary send-pause until you’ve actioned the cleanse. Mailchimp also enforces account-level historical bounce thresholds, accounts with sustained 5%+ over 90 days have been suspended outright. Don’t ignore the email.
What should I do when bounce rate breaches 5%?
Stop campaign sends to your full list immediately. Use Mailchimp’s “Manage Contacts” → filter by “Members who haven’t opened in 180+ days” → archive them. This shrinks the audience by typically 30-40% but the bounce rate on the next send will drop below 2%. Do not unsubscribe-then-resubscribe; do not wipe and re-import. Both are Compliance violations.
Does this card include Customer Journey email bounces?
Yes, Customer Journey emails are pulled from GET /3.0/automations/{workflow_id}/emails/{email_id}/reports. Mailchimp also runs Postcards (physical mail) and SMS through the same product UI, neither has a “bounce” concept and neither contributes here.
Why is my bounce rate higher than Klaviyo benchmark?
Mailchimp’s list-first model encourages broader sends to less-segmented audiences than Klaviyo. A “send to entire audience” on Mailchimp routinely hits 3x more dormant addresses than a Klaviyo segmented send to “active 60D” segment. The fix is segmentation, not platform-switching. Restructure your sends to use Mailchimp’s “engaged subscribers” filter (60d active opens or clicks) and bounce rate normalises within 2-3 sends.
Why does my bounce rate spike on Mondays?
B2B-heavy lists do this 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. If your Monday rate is consistently 1.5-2x the rest of the week and your audience skews B2B, that’s why.
My account uses a custom sending domain via Mailchimp Authentication, does that affect bounces?
The bounce rate doesn’t change but the consequences do. With a custom authenticated subdomain, reputation damage is contained to that subdomain and doesn’t bleed into your main store domain’s transactional email. Without one, throttling on Mailchimp’s shared infrastructure can ripple into order-confirmation emails. If you regularly run >3% bounces, set up domain authentication.
What’s the difference between bounces and “Compliance” suspensions?
Bounces are SMTP-layer rejections (delivery failures). Compliance suspensions are policy-layer actions Mailchimp imposes when bounce rate, complaint rate, or list-quality flags trigger automated review. Compliance can pause your account even when bounce rate is just under 5% if other signals (low engagement + fast list growth from purchased sources) raise red flags.