Klaviyo deliverability: what to check and why it matters

The short answer

Deliverability holds when five signals stay healthy: bounce rate, spam complaints, list engagement, authentication and cadence. The work is a monthly reading of those five, an engagement-segmented sending policy that protects them, and a sunset flow that retires the audience that has left. None of it is difficult, and the brands that do it never have the six-month repair project this article ends with.

Why deliverability decays invisibly

Deliverability rarely fails suddenly. It degrades over months, driven by an accumulation of small negative signals, bounces from stale addresses, spam complaints from disengaged subscribers, sends to contacts who stopped opening years ago. Each one is minor on its own, but together they shift how inbox providers view the sender.

By the time open rates have dropped meaningfully, the reputation damage is already done and takes time to repair. The brands that hold strong deliverability are the ones managing the signals before they accumulate, and Klaviyo now surfaces most of them in one place through its deliverability hub.

The mechanism worth understanding is that inbox providers score the sender rather than the individual email. Gmail's filters are evaluating the sending domain's history when they place a message, which is why one clean campaign cannot rescue a damaged reputation and one bad send to a stale list can start a slide that takes a quarter to show up fully.

The requirements floor since February 2024

Google and Yahoo turned several best practices into hard requirements for bulk senders from February 2024, and they are the floor everything else stands on.

• Authentication: SPF, DKIM and DMARC on the sending domain, covered step by step in our authentication setup guide.
• One-click unsubscribe in the message headers, honoured within two days, which Klaviyo handles for list emails automatically.
• Spam rate in Google Postmaster Tools kept below 0.1 percent, and never touching 0.3 percent, the level at which Gmail starts refusing delivery.

A sender missing any of these is not competing on content quality, because the mail is being filtered on arrival. Verify all three before reading any other metric, since every downstream signal is noise while the floor is missing.

The five signals, and how to read them

Bounce rate deserves one nuance: Klaviyo suppresses hard bounces automatically, so the reading to watch is the rate on each send rather than a cumulative figure, and a climb on regular campaigns means the acquisition sources feeding the list need auditing before the campaigns do.

Cadence cuts both ways. Sending less than monthly lets subscriber memory fade, so complaint rates spike when a campaign finally lands, while sending daily to an unsegmented list saturates engagement and converts tired subscribers into unsubscribes and complaints. The rhythm matters more than the frequency, because forgotten permission comes back as complaints.

Engagement segmentation: the policy that protects everything

The single structural protection is sending by engagement window rather than to the list. Build segments at 30, 60, 90 and 180 days of engagement, defined by opens, clicks or site activity, and give each a sending tier: the 30 and 60-day segments receive everything, the 90-day segment receives the strongest campaigns, the 180-day segment receives occasional sends designed to re-qualify engagement, and beyond that nobody hears from you outside the sunset flow.

This is how the engaged share of the list stays the audience inbox providers see. The brands in chronic deliverability trouble are almost always sending everything to everyone, where every campaign is an invitation for the disengaged majority to file complaints that outweigh the engaged minority's opens.

One measurement caveat keeps the segments honest: opens are inflated wherever Apple's Mail Privacy Protection prefetches images, so an opens-only engagement definition overstates the healthy audience. Build the windows on clicks and site activity alongside opens, and treat click reach as the harder currency.

The sunset flow

A sunset flow is an automated sequence that makes a final attempt to re-engage subscribers who have gone quiet, then suppresses the ones who do not respond. Klaviyo's own guidance builds the segment around profiles that have received a meaningful number of emails over an extended period without a single open, click or purchase.

The build is small: entry from that segment, one or two properly strong re-engagement messages, a wait step measured in weeks, then automatic suppression of the profiles that stayed silent. The emails themselves should be the best offer or the plainest question you are willing to send, because this is the last conversation, and a weak "we miss you" wastes it.

Most brands do not have one, so the list grows while the engaged proportion shrinks. A well-built sunset flow stabilises that ratio, it stops the slow decay that comes from sending to an audience that has already left, and it shrinks the bill on a platform priced by profile count, which is the rare deliverability fix that pays for itself in cash as well as reputation.

The monthly monitoring routine

1. Read the Klaviyo deliverability hub for the trend on opens, clicks, bounces, spam rate and unsubscribes, by campaign and by inbox provider.
2. Read Google Postmaster Tools for the spam rate and domain reputation Gmail itself reports, because Gmail is usually most of the list.
3. Check the engaged-share trend: the 90-day engaged segment as a proportion of the sendable list, which is the single number that predicts trouble earliest.
4. Scan the flows nobody looks at, since a broken trigger or an ancient flow sending to unengaged profiles can quietly generate complaints all month.

Twenty minutes a month, and the point is the trend rather than any single reading. Deliverability problems announce themselves quarters in advance to anyone reading these four places.

If placement is already lost

The repair route is contraction. Pause sending to everything beyond the 30-day engaged segment, fix the floor if any of it is missing, and send your best content to that core until the metrics recover, then re-expand one engagement window at a time exactly as if warming a new domain, because reputation repair and reputation building are the same process.

Expect the timeline in months. Inbox providers extend trust on sustained evidence, there is no appeals process and no shortcut through a new domain, since a fresh domain sending to the same damaged list rebuilds the same reputation with a cold start added. The honest cost of repair is the strongest argument for the twenty minutes of monthly prevention.

Questions we hear about deliverability