On reliability alone, Mailchimp wins the current window: 100% uptime with zero major incidents over the 180 days ending July 2026, against Klaviyo's 99.81% (B+ grade) with 2 major incidents totaling 326 minutes of downtime, most of it from the May 2026 outage that halted campaigns and flows during business hours.
The numbers, side by side
| Metric (180 days ending July 2026) | Mailchimp | Klaviyo |
|---|---|---|
| Uptime (major/critical incidents) | 100% | 99.81% |
| StatusBird reliability grade | A+ | B+ |
| Major or critical incidents | 0 | 2 |
| Total downtime | 0 minutes | 326 minutes |
How these numbers are measured: StatusBird checks each service's status every 2 minutes, around the clock. Uptime counts major and critical incidents over the 180 days ending July 2026; brief degraded periods are excluded so chronically noisy status pages do not distort the comparison. Full details on the methodology page.
How reliable is Mailchimp?
A clean 180 days: no major or critical incidents recorded. Live history is on the Mailchimp reliability page, with the longer view in is Mailchimp reliable.
How reliable is Klaviyo?
Klaviyo's B+ reflects 2 real incidents, the larger being the May 2026 outage (full timeline in the Klaviyo May 2026 postmortem). Context and history: is Klaviyo reliable and the Klaviyo reliability page.
Should reliability decide between Mailchimp and Klaviyo?
For most stores, no: Klaviyo's e-commerce feature depth is why merchants choose it, and a B+ is a solid grade. The real lesson is operational. An email platform outage during a planned send is silent lost revenue, so whichever you pick, know within minutes when it degrades, especially in Q4. If Klaviyo goes down mid-send, the playbook is in what to do when Klaviyo goes down.
Start monitoring your stack free with StatusBird: 1 service, no credit card required. Pro is $29/month for all 84 services with SMS, email, Slack, Teams, and Discord alerts within 2 minutes of a status change.