Why Your Klaviyo Emails Go to Spam and How to Fix Deliverability (UK Guide)

Your Klaviyo dashboard shows a healthy open rate, your creative is sharp, and yet sales from email feel soft. The likely culprit is deliverability — the one metric that sits underneath every other number and stays invisible until it turns catastrophic. If 15% of your emails land in spam or the Promotions tab, your real performance is 15% lower than the dashboard suggests. A brand with 85% inbox placement and great creative will always lose to one with 98% placement and merely decent creative.

This guide sets out why Klaviyo emails end up in spam and exactly how UK ecommerce brands fix it — from authentication rules that became mandatory in 2024 and 2025, to list hygiene, sunset flows, and Klaviyo's structured recovery path.

Deliverability is the foundation that all other email performance sits on. Open rates, click rates and revenue are all downstream of one question: did the email actually reach the inbox? Platform dashboards rarely surface this, because they report on emails that were accepted by the receiving server — not on whether those emails landed in the primary inbox, the Promotions tab, or the spam folder.

That gap is where brands quietly lose money. The fix is not more clever subject lines. It is understanding how inbox providers decide who they trust, and then systematically removing the reasons they might not trust you.

Klaviyo frames sender reputation as trustworthiness that inbox providers assess using multiple weighted factors. Of those factors, recipient engagement carries the strongest weight. When subscribers open, click and reply, providers read that as a signal your mail is wanted. When they ignore or delete it, the signal runs the other way.

Engagement is the key to the inbox. Providers watch what your recipients do — and act on it.

This is why the single most important first step for most accounts is suppressing profiles that have never engaged. Every send to a dead contact drags your engagement signals down and tells providers your list is stale. Klaviyo makes this straightforward with a Never Engaged segment inside the Deliverability Hub. Suppress those profiles and your remaining sends look far more wanted — which is exactly what raises placement.

Authentication used to be a best-practice nicety. It is now a hard requirement. Google and Yahoo began enforcing bulk-sender requirements — SPF, DKIM and DMARC — in February 2024. Microsoft followed with DMARC enforcement from May 2025. As of 2026, non-compliant bulk email can be rejected outright rather than merely sent to spam.

Klaviyo's core fixes are direct:

• Stop using @gmail.com or @yahoo addresses in your "from" field. Switch to a domain you own. Free consumer addresses fail modern authentication checks and mark you as a bulk sender who does not control their own domain.
• Set up a branded (dedicated) sending domain. This lets you build reputation on your own domain rather than shared Klaviyo domains, and it unlocks DMARC. It is a requirement for bulk senders emailing Gmail and Yahoo recipients.
• Align your click-tracking domain with your sending domain. Using the same root domain across both makes your sends look more trustworthy to inbox providers.

None of this is cosmetic. Without a branded sending domain and correct authentication, you are increasingly likely to have mail bounced at the door — not filtered, rejected.

You cannot fix what you do not measure against. Klaviyo's UK 2026 benchmarks, drawn from over 183,000 brands, put the average email campaign open rate across all industries at 31%, with the top 10% hitting 45.1%. Average automated flow click rate is 5.58%, with the top 10% at 10.48%.

Flows consistently outperform campaigns because they trigger at the right moment with relevant content. Independent analyses of Klaviyo data report flows averaging roughly 42%+ open rates versus 31% for campaigns, 5.58% click versus 1.69%, and a 2.11% placed-order rate versus 0.16%.

Deliverability health targets

These are the numbers to hold your account to:

• Delivered rate 98%+ and inbox placement of 95%+.
• Bounce rate below 2% — best-in-class flows sit under 0.35%. Above 5% is a red flag to ISPs; above 10% and they start blocking you.
• Spam complaint rate below 0.1%. Google's damage threshold is often cited around 0.08%, so keep well clear.
• Unsubscribe rate below roughly 0.3% per send.

An unsubscribe is infinitely better than a spam complaint. One quietly trims your list; the other poisons your reputation.

At least 25% of an email database decays every year — people change jobs, abandon addresses, and lose interest. Ongoing cleaning is therefore not a one-off project but a routine. A smaller, healthier list will outperform a bloated one every time.

Practical steps:

• Enable automatic hard-bounce suppression. Klaviyo also auto-suppresses profiles after 7 consecutive soft bounces.
• Segment by engagement tiers. Send to 30/60/90/120-day engagement windows rather than blasting the full list on every campaign.
• Give new subscribers a grace period. Around six months before you judge them on engagement, so you do not suppress genuine prospects too early.

How often you clean depends on volume. High-volume senders pushing 100,000+ emails a month should clean monthly. Smaller senders can clean quarterly and stay healthy.

A sunset flow is your automated exit ramp for subscribers who have gone quiet. Target people who have not engaged in 90–120 days with a short re-engagement sequence. Those who click or open are folded back into your active segments; those who do not are suppressed cleanly, before they become the dead weight that drags placement down.

Pair this with engagement-tier sending as your default operating model. Instead of emailing everyone with everything, you send more to your most engaged tiers and less — or nothing — to those drifting towards inactivity. This keeps your aggregate engagement signals strong, which is precisely what providers reward with inbox placement.

If placement has already collapsed, Klaviyo provides a structured recovery path. To strengthen your standing with a specific inbox provider, remove low-performing domains from your regular sends for the next 3–5 campaigns and send separately only to recently engaged profiles on that domain.

During repair, tighten everything:

• Set winback, re-engagement and sunset flows to draft. These typically see lower engagement, which works against you mid-repair.
• Pause any third-party marketing. Keep your sends to owned, engaged audiences only.

For qualifying accounts, Klaviyo's Reputation Repair AI can automatically exclude unengaged profiles. Prerequisites include a deliverability score below 50, at least 5,000 active profiles, at least 100 clicks or opens in the last 30 days, and a campaign of 1,000+ recipients in the last 30 days. The process sends in phases — 30, 60, 90 and 120-day engaged windows — expanding as your score improves, and aims to finish at a deliverability score of 75 or above.

New senders and newly registered domains — anything within 30 days — must warm the sending infrastructure over the first 2–4 weeks. You start with small volumes to your most engaged contacts and scale up gradually, so providers see a consistent, wanted pattern rather than a sudden blast from an unknown domain. Klaviyo offers guided warming for eligible accounts.

Once established, let engagement dictate cadence rather than a fixed schedule:

• Daily can suit your highly engaged customers.
• Roughly 3x a week for those who have not engaged in 30 days.
• Once a week for those inactive for 90 days.

Matching frequency to interest keeps your best relationships warm without burning out the contacts on the edge of unsubscribing.

Deliverability is not a technical afterthought — it is the ceiling on everything else your email programme can achieve. Authenticate properly, because the rules are now enforced and non-compliant mail gets rejected. Suppress the profiles that never engage, clean your list on a schedule, and run sunset flows so decay never accumulates. Measure against real targets: 98%+ delivered, under 0.1% complaints, 95%+ placement.

Do that consistently and you stop guessing why sales are soft. A smaller, engaged, well-authenticated list will out-earn a bloated one every single send — and the brand that reaches the inbox is the brand that gets paid.