Apple MPP inflates this number. Pair with click_to_open_rate for a truer engagement signal.
At a glance
The percentage of delivered emails that were opened, aggregated across every campaign and Customer Journey email sent in the period. Computed asSUM(unique_opens) ÷ SUM(emails_sent) × 100from thereports.opensblock on each campaign report. Apple’s Mail Privacy Protection inflates this metric. UK consumer lists with heavy iOS Mail usage routinely report 50-70% open rates that are 30-40% higher than actual reads. Pair with Click-to-Open Rate for a truer engagement signal.
| What it counts | SUM(unique_opens) ÷ SUM(emails_sent) × 100 across every campaign + Customer Journey email in the period. Pulled from GET /3.0/reports/{campaign_id}.opens.unique_opens and the matching emails_sent. |
| API endpoint + field | Marketing API v3. reports.opens.unique_opens is the numerator; reports.emails_sent is the denominator. Mailchimp aggregates server-side per object. |
| Audience-based vs segment-first | Mailchimp aggregates open rate per-audience (or per-segment-of-audience). This card sums opens and sends across every audience to produce one account-level number. Per-audience open rates can vary wildly (B2B audiences often open at 40-50%, dormant cleanup tiers at 5-10%); the blended figure hides this. Use Audiences Overview to see the split. Klaviyo’s segment-first model surfaces these splits more naturally; Mailchimp users typically have to drill in. |
| Channel scope | Email only. Mailchimp Studio SMS opens (where supported) are not pulled here. Postcards have no open concept. |
| Open definition | Unique opens. Mailchimp counts a single open per recipient per campaign regardless of how many times they re-open. The pixel fires on image load, so plain-text emails and image-blocked clients (e.g. corporate Outlook with images-off default) under-report opens here. |
| MPP impact | Significant. Apple Mail Privacy Protection (introduced iOS 15, Sep 2021) pre-fetches images server-side, firing the open pixel even when the user never opens the email. UK consumer lists are typically 50-70% Apple Mail; expect 30-40% inflation. Mailchimp does NOT label MPP-attributable opens, unlike some ESPs. A “70% open rate” today on a Gmail-heavy list is plausible; on an iOS Mail-heavy list it’s largely robots. |
| Bounce handling | Bounces are excluded from the denominator (emails_sent already excludes bounces). Hard and soft bounces both removed. |
| Attribution model | Not applicable. Open rate is a send-side engagement metric, not a conversion metric. |
| Currency | Not applicable. |
| Time window | 30D vsP (default 30D vs the prior 30D) |
| Alert trigger | <10% (drives sentiment_key: open_rate). At <10%, even MPP-inflated lists are unhealthy, expect deliverability problems imminent. |
| Roles | owner, marketing |
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 non-profit charity newsletter on Mailchimp with a single audience of 24,000 subscribers (predominantly UK consumer, mixed iOS/Android/desktop). The 30-day window covers 03 Apr 26 to 02 May 26.| Campaign | Sent | Unique opens | Open rate |
|---|---|---|---|
| Spring fundraising appeal | 23,400 | 14,820 | 63.3% |
| Volunteer event reminder | 8,200 | 5,680 | 69.3% |
| Quarterly impact report | 22,900 | 14,650 | 64.0% |
| Donor thank-you (Customer Journey) | 1,200 | 920 | 76.7% |
| Account total | 55,700 | 36,070 | 64.8% |
- The headline 64.8% looks fantastic but ~25-30% of those opens are MPP robots. UK charity lists often skew older and more iOS-heavy than typical DTC. Strip out the MPP inflation and the real open rate is closer to 45-50%, still healthy for a non-profit but not the trophy figure the dashboard suggests. Always pair this card with Click-to-Open Rate and Click Rate, MPP doesn’t fake clicks.
- The Customer Journey thank-you email opens at 76.7%, the highest in the account. This is normal: triggered transactional-style emails are highly anticipated by the recipient (they just donated, they expect a confirmation), so genuine open intent is high AND MPP inflates further. Customer Journey opens routinely beat broadcast campaigns by 10-15 percentage points.
- The volunteer reminder beat the broadcast appeals slightly. This is typical of segmented sends, the volunteer reminder went to a smaller, more engaged sub-audience. List-based blast vs segmented send efficiency shows up here. Mailchimp’s list-first model means small segmented sends like this require more setup than they would on Klaviyo, but the engagement payoff is similar.
- A 1% drop-off from 65% to 64% is not significant. Open-rate noise band is roughly ±2-3 percentage points week-over-week on a list this size. Don’t chase the daily figure. Watch the 30D rolling vs the prior 30D, the alert threshold is <10% which is a different order of magnitude.
- The same campaigns sent 12 months ago (pre-MPP) would have shown 38-45% open rates. Historical comparisons across the iOS 15 boundary (Sep 2021) are unreliable. If you have a “but our open rate used to be 40%” reference point from before late 2021, the apples-to-apples replacement metric is now click rate, not open rate.
Sibling cards merchants should reference together
Open rate is MPP-noisy. Pair it with these for real engagement signal:| Card | Why pair it with Open Rate |
|---|---|
| Mailchimp Click Rate | The MPP-resistant signal. Apple’s pre-fetch fires opens but does NOT click links. Click rate is your true engagement metric. |
| Mailchimp Click-to-Open Rate | clicks ÷ opens. Strips MPP-inflated opens out of the denominator. CTOR > 10% is healthy regardless of raw open rate. |
| Mailchimp Bounce Rate | The denominator pair. If bounces spike, opens drop because more sends fail to land. Watch them together. |
| Mailchimp Spam Complaint Rate | The other half of deliverability. Low opens + rising spam = list quality crisis; low opens + flat spam = content/cadence problem. |
| Mailchimp Audience Size | Open rate falls as audiences grow with less-engaged subscribers. Pair to spot list-fatigue patterns. |
| Mailchimp Email-Attributed Revenue | Open-rate moves typically lead revenue by 1-2 weeks. A persistent open drop predicts revenue dip. |
| Mailchimp Audiences Overview | Per-audience open rate split. Hides important variation behind the blended figure. |
| Mailchimp Top Campaigns by Revenue | The campaigns winning revenue often have the best open + click combo, not the best open alone. |
Reconciling against the vendor’s own dashboard
Where to look in Mailchimp’s own dashboard: Mailchimp → Audience → All Contacts → Recent Activity for per-subscriber open history, and Mailchimp → Campaigns → Reports for the per-campaign Open Rate metric. The headline tile on each campaign report shows “Opens” and “Open rate”, and the Audience Overview panel shows the rolling rate. This card sums opens and sends across every campaign + Customer Journey email in the period to one figure; figures should match this card to within ±0.2 percentage points. Other Mailchimp views that look like the same number but aren’t:- Audience → Settings → Audience health: a different “open rate” computed against the audience’s most recent send only. Different denominator.
- Reports → Comparative Reports: ad-hoc selection. Defaults differ from this card’s “every campaign + automation in window” rule.
- Customer Journeys → individual journey → email step: per-email-step open rate, not aggregate.
| Reason | Direction of divergence |
|---|---|
| Time-zone. Mailchimp uses the merchant’s account timezone (set in Account → Settings → Details). Vortex IQ uses UTC by default. Boundary days differ. | ±0.1-0.3 pp at the boundary |
| Audience-vs-list aggregation. Per-audience views in Mailchimp show smaller subset numbers; the “All Contacts” rollup matches this card. | Per-audience views are LOWER than this card; the all-audience rollup matches |
| Page caps. Engine pages campaigns 10 per call, up to 5 pages (50 total). Accounts running >50 distinct campaign sends per 30D will see truncated denominators. The blended rate stays directionally correct. | Vortex IQ slightly off for very high-cadence senders |
| MPP timing. Apple’s pre-fetch happens within minutes of delivery. A campaign sent at 23:55 UTC may have its pre-fetched opens fire just after midnight, landing on a different day in Mailchimp’s tz vs Vortex IQ’s UTC. | None on the 30D total |
| Customer Journey aggregation. Mailchimp’s per-journey rollup sometimes shows averaged open rate across steps; Vortex IQ pulls per-email-step opens and sends, then aggregates. The math should match but per-step views differ. | None on the headline |
| Card | Expected relationship | What causes legitimate divergence |
|---|---|---|
klaviyo.klv_open_rate | If both ESPs run on the same store with similar audiences, Klaviyo open rate typically tracks within ±5 pp of Mailchimp. | Klaviyo’s segment-first send strategy means more frequent small sends to engaged segments, often producing slightly higher blended rates. Different MPP-detection logic at the ESP level can also nudge the number. |
| Gmail Postmaster Tools (no connector) | Gmail’s “domain reputation” should track engagement directionally. Postmaster shows ISP-side; Mailchimp shows sender-side. | Postmaster has Gmail-only visibility; Mailchimp has all-ISP. |
Known limitations / merchant FAQs
Why is my open rate 65%? Is that real? Almost certainly not. Apple Mail Privacy Protection pre-fetches images server-side, firing the open pixel without any human reading the email. UK consumer lists with heavy iOS Mail usage routinely show 50-70% open rates that are inflated by 30-40% over the genuine read rate. Your “real” open rate is closer to 40-45%. Use Click Rate and Click-to-Open Rate for the MPP-resistant truth. Why are my open rates lower than Klaviyo’s? They might not be, properly. Both ESPs use unique-opens with image pixels, both are MPP-affected. The most common cause of a lower Mailchimp blended rate is list-wide blasts (Mailchimp’s default sending pattern) vs segmented sends (Klaviyo’s default). A list-wide blast hits dormant subscribers who don’t open; a segmented send only hits engaged subscribers who do. Restructure sends by segment in Mailchimp to close the gap. My open rate dropped 10 percentage points. What happened? Three usual causes: (a) you imported a large batch of new subscribers without confirmation, diluting the engaged base; (b) a deliverability problem dropped you into the spam folder for one major ISP (typically Gmail), where opens still fire but at lower volume; (c) you changed sending domain or sender name, breaking subscriber recognition and triggering low engagement on the first few sends. Open Mailchimp → Account → Sender Reputation to check, and pause sends if reputation has dropped below “Good”. What’s a healthy open rate for Mailchimp specifically? Post-MPP (i.e. since late 2021), the “healthy band” for consumer DTC on Mailchimp is roughly 30-45%, but the band is misleading because of the MPP inflation. A more honest framing: a healthy Mailchimp account has Click Rate >2% and Click-to-Open Rate >8%. If those two are healthy, raw open rate is window dressing. The alert threshold here (<10%) is set deliberately low because below that, even MPP can’t save you, the list is genuinely dead. Why do triggered Customer Journey emails open higher than broadcast campaigns? Triggered emails are anticipated. The customer just signed up, just abandoned a cart, just placed an order, they’re expecting the email and engaged with the brand at the moment. Broadcast campaigns interrupt; triggers respond. Customer Journey opens of 50-80% are normal and don’t require a benchmarking adjustment. Does this card include opens from automation/Customer Journey emails? Yes. This card sums opens and sends across regular campaigns, A/B test variants, and every Customer Journey email step that delivered in the period. Why is my today value volatile? Today’s open rate is computed against partial-day sends. If you sent at 09:00 UTC and it’s now 12:00 UTC, MPP pre-fetches have fired but human opens through the day haven’t accumulated. Treat today as directional only. Does Mailchimp distinguish MPP opens from real opens? No. Unlike some ESPs that flag pre-fetched opens server-side, Mailchimp’s API returns a singleunique_opens figure with no MPP attribution. To estimate the inflation, look at the gap between Open Rate and Click-to-Open Rate, if your CTOR is <8% but your open rate is >50%, MPP is doing most of the work.
What about plain-text or images-blocked clients, do they under-count?
Yes. Corporate Outlook with images-off is the classic case, recipients open and read the email but the pixel never fires, so they’re invisible to this metric. B2B audiences are 20-40% under-counted on opens for this reason. Don’t penalise B2B campaigns for “low” open rate; check the click rate instead.