On March 18, 2026, Klaviyo's email sending infrastructure experienced a major outage lasting 5 hours and 25 minutes. Campaigns appeared to send. Dashboards showed normal activity. But emails were not arriving in inboxes. For stores with morning campaigns scheduled that Tuesday, the revenue impact was significant and, in most cases, entirely unrecoverable.
Timeline of the March 18 Klaviyo outage
6:08 AM UTC: Klaviyo's Email Sending API begins degrading. European stores are the first to notice delivery failures, but most US-based merchants are asleep or just starting their day.
7:22 AM UTC: Klaviyo posts a status update: "Investigating issues with email delivery." The status is listed as "Degraded Performance" rather than outage, which understates the scope of what is actually happening.
8:15 AM UTC: Status upgraded to "Major Outage" affecting Campaign Sends. Flow triggers are also partially affected. SMS sending is unaffected. The Klaviyo dashboard continues to show emails as "sent" with no errors surfaced to merchants.
11:33 AM UTC: Klaviyo posts resolution. A backlog of queued emails begins processing. Duration: 5 hours 25 minutes.
The "silent send" problem
What made this outage particularly damaging was the failure mode. Klaviyo did not return errors. It did not mark sends as failed in your dashboard. Emails entered a send queue that looked normal from the inside but was not delivering to recipients.
A merchant who checked their Klaviyo dashboard at 9 AM would have seen their scheduled campaign with a "Sending" or "Sent" status, a reasonable-looking recipient count, and no error indicators. The first signal that something was wrong often came hours later, when email revenue did not show up in Shopify analytics and open rates were zero.
This is what makes Klaviyo outages systematically more expensive than, say, a Stripe outage. Stripe failures are loud. Checkout breaks visibly. Klaviyo failures are quiet. You think you sent 18,000 emails. You sent zero.
Why Tuesday morning was the worst possible time
Tuesday is the most common day for scheduled marketing campaigns across e-commerce. Many stores schedule their weekly promotional email for 7 to 9 AM local time (12 to 2 PM UTC). The March 18 outage hit squarely in that window.
Klaviyo does not automatically resend campaigns that fail during an outage. Once a campaign's send window closes, the missed emails are gone. You can manually resend to the original list later, but a Tuesday morning promo that arrives Thursday afternoon performs a fraction as well. The revenue is largely lost.
Abandoned cart flows and the compounding effect
Beyond campaigns, flow-based emails were also partially affected. Abandoned cart sequences, browse abandonment triggers, and post-purchase flows that were supposed to fire during the 6-hour outage window either didn't trigger or triggered but failed to deliver.
Abandoned cart emails are typically worth 5 to 15% of the recovered cart value. A store with $5,000 in abandoned carts during that window and a 10% recovery rate lost roughly $500 in attributable email revenue from flows alone, on top of whatever campaigns were silently dropped.
The revenue math
Consider a mid-size Shopify store with a 25,000-subscriber list running a spring sale campaign that Tuesday morning:
- Campaign to 25,000 subscribers, expected 22% open rate, 3% click rate, 2% conversion on clickers
- Average order value of $75
- Expected revenue from that campaign: approximately $1,125 to $2,250 depending on list engagement
- Revenue from the campaign after the outage: zero, if it landed in the silent-send window
For larger stores with engaged lists and higher AOV, the number scales quickly.
Klaviyo's outage frequency
Klaviyo has recorded over 440 incidents across its lifetime as of mid-2026. Not all involve email sending. But delivery and flow failures are not rare events — they occur multiple times per year, often clustering around periods of high send volume such as product launches, promotional periods, and post-holiday follow-up windows.
The March 18 incident was notable for its duration and timing but not for being unusual. Klaviyo, like every major email infrastructure provider, has incidents. The cost of those incidents correlates directly with how quickly you know about them.
What to do when Klaviyo has an outage
- Know immediately. The worst outcome is finding out 4 hours later because your Tuesday email revenue was zero. StatusBird monitors Klaviyo every 2 minutes and alerts you via SMS, email, or Slack the moment the status changes.
- Do not schedule new campaigns. If you know Klaviyo is degraded, hold any campaigns you were about to send. Send them once delivery is confirmed restored.
- Check your delivery data after recovery. Do not trust the "Sent" count in Klaviyo's dashboard. Check delivery rates and actual opens for sends during the outage window. If delivery rate is near zero, the campaign did not go out.
- Decide on a resend. For high-value campaigns, a same-day resend after resolution is often worth it. Acknowledge the delay with a light-touch subject line rather than resending the identical email.
- Audit your flow backlog. Check whether abandoned cart, browse abandonment, and post-purchase flows fired normally during the outage window. Missing triggers typically cannot be retroactively re-sent, but knowing the gap helps you estimate total impact.
The March 2026 outage cost a lot of Shopify stores meaningful revenue, most of it silently. Monitoring Klaviyo's status is table stakes for stores where email is a primary revenue channel.