You might assume that if you send the exact same email through Klaviyo and Mailchimp, the results would be nearly identical. After all, the content doesn’t change. But when you look at the reports, you often notice something surprising: the performance numbers aren’t the same. Open rates, click-through rates, and even spam complaints can vary significantly between the two platforms.
This discrepancy leaves many marketers scratching their heads. If the copy, design, and offers are the same, what explains the gap? The answer lies in deliverability, infrastructure, and how each Email Service Provider (ESP) interacts with Gmail, Outlook, Yahoo & more.
Delivery Isn’t the Same as Deliverability
Both Klaviyo and Mailchimp will “deliver” your message to the recipient’s mail server about 98% of the time. But delivery simply means that your message didn’t bounce. Deliverability is the real measure that determines where your email lands: Primary, Promotions, Spam, or not at all (blocked).
Deliverability is usually measured in terms of open rates. Make sure you look at open rates instead of delivery rates.
iOS 15 Discrepancies
If you think you’re getting 50%+ open rates on your average campaign, you’re probably not. Apple released an update in September 2021 that has slowly yet falsely inflated open rates by setting off open triggers in marketing emails due to “privacy concerns”. By now, most users are running iOS 15 or newer, which means that open rates are showing as inflated compared to before the update.
Fortunately, most ESPs have a box you can check to view your open rates without false iOS 15 opens. Make sure you’ve got the box checked on both Klaviyo and Mailchimp before you compare open rates so that you have a true apples-to-apples comparison.
Shared vs. Dedicated Infrastructure
One major factor is the sending infrastructure each platform uses.
Mailchimp often routes users through large, shared IP pools. This means your sender reputation can be influenced by thousands of other marketers using the same system. If one sender is careless, it can impact everyone else.
Klaviyo, on the other hand, is built with e-commerce brands in mind. It tends to encourage faster upgrades to dedicated sending domains and IPs. That gives you more control, but it also means poor setup or inconsistent sending patterns can directly hurt your own results.
In short, Mailchimp might feel more forgiving because you’re hidden in the crowd, while Klaviyo exposes the true impact of your practices.
Authentication Differences
Inbox providers use authentication to verify that you are who you say you are. SPF, DKIM & DMARC records act like digital signatures on your email.
Mailchimp automatically sets up some authentication for shared domains, which can give the appearance of smoother deliverability. Klaviyo requires you to configure domain authentication if you want maximum performance. That means your Klaviyo results will only be as strong as your setup. If you skip this step, inbox placement can suffer dramatically.
Make sure you’ve got a valid SPF and DKIM record for both Klaviyo and Mailchimp – and a valid DMARC policy for your domain.
Want to check your authentication protocols? Use a SPF, DKIM & DMARC checker to see your setup.
Engagement Signals
Inbox providers also track how recipients interact with your emails. High opens, clicks, and replies build a positive sender reputation. Low engagement signals the opposite.
Mailchimp has long been associated with newsletters and broad audiences, so your campaigns might land in Promotions but still generate decent opens. Klaviyo is more focused on transactional and automated flows (like abandoned cart or post-purchase sequences), so inbox providers may treat those differently.
If you notice higher engagement in Mailchimp but lower placement in Klaviyo, it could be because you haven’t optimized your list segmentation, frequency, or warmup strategy in Klaviyo.
Content Is Filtered Differently
Spam filters don’t just evaluate your infrastructure; they also scan your content. Two ESPs may format your email slightly differently when generating the final HTML. Something as simple as how links are tracked or how images are referenced can change the way spam filters score your message.
That means your identical copy in Mailchimp and Klaviyo isn’t actually identical once it hits the inbox. Mailchimp may wrap links one way, while Klaviyo uses a different system. One format might trigger filters more than the other, even though you never touched the words.
How to Diagnose Performance Differences
When you see Klaviyo and Mailchimp producing different results, don’t assume one tool is better. Instead, investigate:
- Run Inbox Placement Tests: Use an email deliverability tool for Klaviyo or Mailchimp users to see where your campaigns land across Gmail, Outlook, Yahoo, and other inbox providers.
- Check Authentication: Make sure SPF, DKIM, DMARC, and then BIMI are properly set up for your sending domain, especially in Klaviyo. (You can utilize BIMI checkers, too.)
- Analyze Engagement Trends: Compare not just opens but clicks, replies, and unsubscribes.
- Test Content Formatting: Send the same campaign through both ESPs to test how each handles HTML and links.
This process gives you clarity on whether the difference is due to actual engagement or simply placement issues.
Why Mail Testing Is Critical
The only way to cut through the noise is to run mail tests before sending. By doing so, you can see exactly how Gmail or Outlook is treating your message. Mail testing tools show whether you land in Primary, Promotions, or Spam and diagnose authentication, blacklist status, and content triggers.
That’s why two ESPs with the same content can deliver such different outcomes. It’s not just about the words you write…it’s about the invisible signals that inbox providers evaluate behind the scenes.
The Bottom Line
Your Klaviyo and Mailchimp results don’t match because ESPs are more than just content delivery systems. They each have unique infrastructure, authentication defaults, and formatting quirks that influence deliverability. Add in how inbox providers interpret engagement, and the differences start to make sense.
The good news is that you don’t have to guess. By using deliverability testing, maintaining strong authentication, and focusing on real engagement metrics, you can identify and fix the issues that matter most. The platform you choose will always shape your results, but with the right preparation, you can maximize inbox placement & performance, no matter which ESP you use.