Short answer first: check whether it is Klaviyo before you spend an hour debugging your flows. Klaviyo has had real outages, including 2 major incidents totaling 326 minutes in the 180 days ending July 2026, and during the May 2026 outage campaigns and flows simply did not send for hours (timeline here). If the platform is healthy, then work down this list.
Is Klaviyo itself down or degraded?
Check Klaviyo's live status. Sending delays are Klaviyo's most common degradation mode: the platform accepts your campaign but the queue backs up, which looks identical to "not sending" from your side. If there is an active incident, do not re-send; queued messages typically go out when the backlog clears, and re-sending doubles delivery.
Is the campaign actually scheduled, or stuck in review?
Campaigns held by Klaviyo's content review, an unconfirmed sending domain, or a scheduled send time in the wrong timezone all present as silent non-delivery. Check the campaign's status field first; "Sent" and "Scheduled" are different claims.
Are your flow triggers firing?
For flows, the usual culprits are upstream: the trigger event is not arriving. If your abandoned-cart flow went quiet, confirm the underlying integration is feeding events; a platform or integration outage upstream of Klaviyo stops flows without any error inside Klaviyo. Check each flow message's analytics for "skipped" and review flow filters that may be excluding everyone.
Is it a segment or list problem?
A campaign sent to a segment that evaluates to near-zero recipients looks like a sending failure. Check the segment count before the send, and remember smart sending suppresses contacts who received messages recently.
Is it deliverability rather than sending?
If Klaviyo reports delivered but customers see nothing, the problem is inbox placement, not sending: check spam folder placement, your dedicated domain's authentication (SPF, DKIM, DMARC), and whether a recent list import hurt your sender reputation.
How do I catch the next Klaviyo incident before my send window?
The May outage taught Klaviyo-dependent stores the pattern: the platform degrades, sends stall, and the status page catches up later. Independent monitoring alerts you within about 2 minutes of a status change, which is the difference between rescheduling a send calmly and discovering the failure after your promo window closed. Background on Klaviyo's record: is Klaviyo reliable, and the response playbook: what to do when Klaviyo goes down.
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