How to Improve Email Deliverability in Klaviyo

You can write the most compelling email in the world, but if it lands in spam, nobody sees it. Email deliverability is the unsexy foundation that determines whether your marketing actually reaches your customers. And for most ecommerce brands running Klaviyo, it is an afterthought — until open rates start declining and revenue from email drops.

Deliverability is not a one-time setup. It is an ongoing discipline that combines technical configuration (DNS records), list hygiene (removing disengaged contacts), sending practices (segmentation, frequency), and content quality (avoiding spam triggers). Each factor influences the others, and neglecting any one of them can undermine the rest.

We audit deliverability for every Klaviyo account we manage, and the improvements are often dramatic. Brands that were seeing 15-18% open rates regularly reach 25-35% after implementing the practices in this guide. That is not a marginal improvement — it is the difference between email marketing that breaks even and email marketing that drives significant profit.

What is email deliverability?

Email deliverability is the percentage of your emails that successfully reach the recipient's inbox. It is distinct from delivery rate, which only measures whether the email was accepted by the receiving server (not rejected or bounced). An email can be "delivered" but still land in spam or the promotions tab.

Deliverability is determined by your sender reputation — a score that email providers (Gmail, Outlook, Yahoo, etc.) assign to your sending domain based on how recipients interact with your emails. High engagement (opens, clicks, replies) improves your reputation. Low engagement, spam complaints, and high bounce rates damage it.

Factor	Impact on deliverability	Target benchmark
Bounce rate	High bounces signal poor list quality	Under 2%
Spam complaint rate	Complaints directly damage reputation	Under 0.1%
Open rate	Engagement signals inbox worthiness	20%+ for campaigns
Unsubscribe rate	High unsubs suggest irrelevant content	Under 0.3%
DNS authentication	Proves you are who you claim to be	DKIM, SPF, DMARC all configured

Step 1: Set up DNS authentication

DNS authentication proves to email providers that your emails are legitimately from your domain. Without it, your emails are more likely to be filtered as spam.

DKIM (DomainKeys Identified Mail)

1. In Klaviyo, go to Settings > Email > Domains
2. Add your sending domain
3. Klaviyo provides a CNAME record to add to your DNS
4. Add the record through your domain registrar (GoDaddy, Cloudflare, Namecheap, etc.)
5. Wait for Klaviyo to verify (usually within 24-48 hours)

SPF (Sender Policy Framework)

SPF tells receiving servers which services are authorised to send email from your domain. Add Klaviyo's SPF record to your DNS settings alongside any existing SPF records.

DMARC (Domain-based Message Authentication)

DMARC tells receiving servers what to do with emails that fail DKIM or SPF checks. Start with a monitoring policy and move to a stricter policy once you are confident your legitimate emails are all passing authentication.

As of 2024, Gmail and Yahoo require DKIM, SPF, and DMARC for bulk senders. If you are sending more than 5,000 emails per day without these records, your emails will be blocked or filtered to spam. This is not optional.

Step 2: Clean your existing list

A dirty list is the most common cause of deliverability problems. Here is how to clean it:

1. Remove hard bounces — Klaviyo does this automatically, but verify that bounced contacts are properly suppressed
2. Identify never-engaged contacts — find profiles who have been on your list for 90+ days and have never opened or clicked a single email. Consider suppressing them
3. Remove role-based addresses — addresses like info@, sales@, support@ are rarely monitored and often trigger spam complaints
4. Suppress long-term unengaged — contacts who have not opened or clicked in 120+ days should be moved to a sunset segment
5. Verify high-risk imports — if you have imported lists from other sources, run them through an email verification service before sending

For more on building clean, well-segmented lists, see our email segmentation guide.

Step 3: Build a sunset flow

A sunset flow automates the process of identifying and suppressing unengaged subscribers:

1. Create a segment of contacts who have not opened or clicked any email in the last 60-90 days
2. Set this segment as the trigger for your sunset flow
3. Email 1: "We have not heard from you — are you still interested?" with a clear CTA to stay subscribed
4. Email 2 (7 days later): "Last chance to stay on our list" with an opt-in link
5. After Email 2, if no engagement, automatically suppress the contact

Suppressing unengaged contacts feels counterintuitive — you are reducing your list size. But the maths is clear: a smaller, engaged list delivers better results than a large, disengaged one. Every unengaged contact you email drags down your engagement metrics, which damages your sender reputation, which reduces inbox placement for everyone on your list.

For more on how sunset flows fit into your overall flow architecture, see our flow optimisation guide.

Step 4: Segment by engagement

Not every subscriber should receive every email. Segment your list by engagement level and adjust your sending frequency accordingly:

Segment	Definition	Sending frequency
Highly engaged	Opened or clicked in last 30 days	Every campaign
Engaged	Opened or clicked in last 60 days	Most campaigns
Semi-engaged	Opened or clicked in last 90 days	Key campaigns only
At risk	Last engagement 90-120 days ago	Re-engagement campaigns only
Unengaged	No engagement in 120+ days	Sunset flow only

By default, send campaigns to your engaged segments (opened or clicked in last 60-90 days). Only include semi-engaged contacts for major announcements like sales or new product launches. Never include unengaged contacts in regular campaigns — they belong in the sunset flow.

Step 5: Optimise sending practices

Sending frequency

Find the right balance between staying top of mind and over-messaging. Most ecommerce brands should aim for 2-4 campaigns per week for engaged segments. Monitor unsubscribe rates — if they spike, you are sending too frequently.

Smart Sending

Enable Klaviyo's Smart Sending with a 16-24 hour window. This prevents a subscriber from receiving both a flow email and a campaign email within a short period, reducing fatigue and complaint risk.

Send time optimisation

Use Klaviyo's Smart Send Time feature to deliver emails at the optimal time for each individual subscriber based on their historical engagement patterns. This improves open rates, which in turn improves your sender reputation.

Subject line and content quality

Avoid spam trigger words (FREE!!!, Act Now, Limited Time), excessive capitalisation, and misleading subject lines. Write subject lines that accurately describe the email content. Misleading subjects may boost open rates short-term but increase spam complaints, which destroys deliverability long-term.

For more on Klaviyo account management, see our managed services overview.

Step 6: Monitor deliverability metrics

Track these metrics weekly to catch deliverability issues early:

• Open rate trend — a declining trend over 4+ weeks indicates a problem
• Bounce rate per campaign — any campaign with a bounce rate above 3% warrants investigation
• Spam complaint rate — any increase above 0.1% requires immediate action
• Unsubscribe rate trend — rising unsubs suggest content or frequency issues
• Click-to-open rate — declining CTOR indicates content relevance issues

External monitoring tools

• Google Postmaster Tools — free, shows your domain reputation with Gmail specifically
• Microsoft SNDS — shows your reputation with Outlook and Hotmail
• Mail-tester.com — send a test email to get a deliverability score with specific recommendations

Advanced deliverability tactics

Dedicated sending IP

By default, Klaviyo sends your emails from a shared IP pool. For high-volume senders (100,000+ emails per month), a dedicated IP gives you full control over your sending reputation. However, it requires careful warm-up and consistent sending volume.

Domain warm-up

When setting up a new sending domain or migrating from another ESP, gradually increase your sending volume over 2-4 weeks. Start by sending to your most engaged subscribers only, then gradually expand to less engaged segments. This establishes a positive reputation before you reach the full list.

Feedback loops

Register for feedback loops with major email providers. These notify you when a subscriber marks your email as spam, allowing Klaviyo to automatically suppress them and prevent future complaints from the same source.

Content testing for spam filters

Before sending major campaigns, use Klaviyo's spam test feature or external tools to check your email against known spam filter rules. This catches issues like excessive links, image-to-text ratio problems, or flagged phrases before they affect your deliverability.

Preference centre

Instead of a binary subscribe/unsubscribe choice, offer a preference centre where subscribers can choose email frequency and content types. This reduces unsubscribes by giving people a middle ground between "everything" and "nothing." For a comprehensive approach to flow management, see our segmentation guide.

Common mistakes to avoid

1. Buying or renting email lists

Purchased lists are full of invalid addresses, spam traps, and people who never consented to receive your emails. A single campaign to a purchased list can destroy your sender reputation overnight. Build your list organically through signup forms, lead magnets, and customer purchases.

2. Never cleaning your list

A list that grows but is never cleaned accumulates dead weight — invalid addresses, disengaged subscribers, and spam trap addresses. Quarterly cleaning is the minimum. Monthly is better for high-volume senders.

3. Sending to your entire list every time

Blasting every campaign to every subscriber regardless of engagement is the fastest way to damage deliverability. Always segment by engagement level and exclude unengaged contacts from regular campaigns.

4. Ignoring the data

When open rates decline, many brands respond by sending more emails rather than investigating the cause. More volume to a deteriorating reputation only accelerates the decline. Diagnose the problem first — it is usually either a list hygiene issue, a content relevance issue, or a technical (DNS) issue.

5. No double opt-in

Single opt-in allows invalid or mistyped email addresses onto your list, which increases bounce rates. Double opt-in (requiring email confirmation) ensures every address on your list is valid and genuinely wanted. The slight reduction in signup rate is more than offset by the improvement in list quality and deliverability.

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Email deliverability is not glamorous, but it is the foundation everything else rests on. The most beautifully designed email, the most compelling offer, and the most sophisticated segmentation are all worthless if the email lands in spam.

Start with the technical basics (DNS authentication), clean your list, build a sunset flow, and segment your campaigns by engagement. These four actions alone will measurably improve your inbox placement and, by extension, your email marketing revenue.

Need help diagnosing or fixing deliverability issues in Klaviyo? See our Klaviyo services or get in touch for a free deliverability audit.