The success and failure of any email campaign or automated flow is decided by the deliverability of your messages. It’s the very first hurdle.
Because if your messages are landing in spam (or worse, not being sent) then your recipient is unlikely to see them and open your content. This makes all the time you’ve spent building your template design and crafting your sales messaging a waste of time.
Writing this guide is a Klaviyo Master Platinum partner agency, we fix Klaviyo deliverability issues every single week for our clients. We’re about to go through the exact step our agency uses to diagnose deliverability issues, then explain how to fix them.
Before that, if you would like to skip the hard work and have Email Kong do it for you for free. Then you can follow this link to access our free Klaviyo audit where we will diagnose your email deliverability issues.
How To Diagnosing Your Klaviyo Deliverability Issue
Our agency specializes in using Klaviyo and has in-house frameworks to fix email deliverability errors. We always start by figuring out the precise issues that are causing your email deliverability errors. Below are the five steps we follow, in order, every time.
Step 1: Write Down What Changed In Your Klaviyo Account, And When
Record the first thing you noticed and the date it appeared. You’re looking for things like an influx of new subscribers or a spike in your bounce rate. Essentially anything out of the ordinary in your Klaviyo dashboard.
The exact start date matters a lot. Deliverability faults are usually introduced by a change (think using a new sending domain, or DNS edit). Knowing what that change was, and reversing it, could be all we need to do get your emails landing
Step 2: Read The Bounce Reason In Klaviyo Before Any Other Metric
A bounce carries the receiving server's reason for refusing your message. It is always provided in the form of an error code. Look for the error code and then if you don’t understand it use Google or an AI assistant to explain it to you.
The reason could be something simple like a typo in your DMARC records or it could be that your sending domain has been blacklisted. The error code will let you know and then guide your recovery strategy.
Step 3: Check To See If Your Domain Has Been Blacklisted
Blacklists exist to block domains known for sending spam messages landing in your inbox. They’re many email blacklist providers that give away their full database for free, these free blacklists are the ones currently used by medium and smaller businesses.
If you land on one of these blacklists it's going to cause serious deliverability problems for your Klaviyo campaigns.
Luckily, you can check every free blacklist provider to see if you have been listed. Mx Toolbox has a great free blacklist checker which checks your sender reputation in minutes.
If you have been blacklisted by a certain provider you must reach out to them and follow their guidance to be reconsidered.
One thing also worth knowing is that major mailbox providers use their own internal blacklists that aren’t shared publicly. Recovering your email deliverability on these networks is much more difficult.
Step 4: Use a Seed List to Find the Problem Mailbox Provider
It's possible that your emails might only be bouncing on the servers of specific mailbox providers like Microsoft, Gmail, or Apple. To find out which one we need to run a seed list test.
A seed list is a set of test email addresses that you own. Each one sits with a different provider. One is a Gmail address. One is an Outlook address. One is a Yahoo address. One is an iCloud address. You get the picture.
You get these addresses from a tool such as GlockApps or Inbox Monster. The tool gives you the addresses and watches the inboxes for you.
Here is how you use them. Add the seed addresses to a segment in Klaviyo. Send your campaign to that segment first, before you send it to your customers.
The tool then checks each test inbox and tells you what happened to your email at each provider. It either arrived in the inbox. Or it went to spam. Or it never showed up.
That is the answer this step needs: which mailbox providers accept my emails and which are causing the deliverability problems.
Step 5: Rule Out Bot Clicks Before You Trust Your Engagement Rates
Bot clicks come from security scanners, corporate filters and link-preview tools following links to check they are safe. Your engagement rates count these non human interactions in your Klaviyo reports.
One telltale sign bots are behind your engagement metrics is when your click rate % raises above your open rate %. Or your click rate % rising while orders and sessions stay flat.
Our guide to common email marketing mistakes covers this and more.
Fix Authentication First, Engagement Second, Content Last
Now you know what’s causing your Klaviyo deliverability problems we can move onto the improvements you can make to fix them.
We haven’t chosen this order at random, it's ordered exactly how our agency prioritizes these tasks: based on how quickly they can stop costing you money.
Authentication Faults Break Delivery Overnight And Clear Within Hours
An SPF, DKIM or DMARC fault stops delivery the moment it exists. It is also the only fault on this list that a single corrected DNS record fixes. That correction takes effect as soon as your record propagates.
Both properties explain its position. Damage is total while the fault lasts, and repair is measured in hours. Nothing is gained by working elsewhere first, because a rejected message never reaches a subscriber who could engage with it.
Engagement Damage Takes Weeks Of Consistent Klaviyo Sending To Undo
Klaviyo's own documentation is direct about the weighting. What your recipients do with email sent by your brand has the strongest impact on sender reputation, its guidance states, and engagement is the key to the inbox.
That weighting explains why engagement damage reverses slowly. Once a mailbox provider has recorded weeks of poor engagement, only weeks of better engagement change its assessment. No same-week fix exists.
A list clean carried out on Monday will therefore not produce a different reputation by Friday. Brands that expect otherwise conclude the list clean failed, then revert.
Content Moves Inbox Placement Least
Content is where most people start. Subject lines, spam words and image ratios are the easiest things in the account to change, but changing those works less than you think.
Hazel Village, a Brooklyn maker of ethically produced stuffed animals, holds a Klaviyo deliverability score of 95% while sending email content that is deliberately image-heavy.
Raquel Caticha explains how she created Hazel Village’s Klaviyo templates by using:
- Live-text headers and footers carry the important links
- A transparent PNG logo converts cleanly to dark mode
- Body fonts that are available across every email client or mailbox provider
Hazel Village did not win by changing its content to use fewer images. They won by making the parts of that content which were not images still work, which is the mechanism a text-to-image ratio stands in for.
Content changes of this kind are worth making. Our notes on Klaviyo email template design go further into what makes a winning build.
Check Whether You Are Still Sending From Klaviyo's Shared Domain
A Klaviyo account does not start on infrastructure you own. Klaviyo's documentation on branded versus shared sending domains puts it plainly: by default, you start out sending from a shared IP and shared Klaviyo domain.
Your sending reputation is therefore generated partly by other Klaviyo customers. Half of that setup you can change, and the other half you almost certainly cannot.
Gmail Shows 'via klaviyomail.com' When You Are On The Shared Domain
Which setup you are on can be settled in ten seconds, using an email you have already sent. On a shared sending domain, Gmail displays your sender address with "via klaviyomail.com" attached. Open any campaign you sent to your own Gmail address and look at the sender line.
Seeing that string means you are building reputation on a domain shared with other senders. Any goodwill you accumulate is pooled with theirs. More on how the platform fits together sits in our guide to Klaviyo as a CRM.
Klaviyo Reserves Dedicated IPs For Senders Above A Million Emails A Month
Klaviyo recommends a dedicated IP for accounts consistently sending over a million emails a month, approved case by case. For almost every D2C brand, that puts IP reputation permanently outside your control.
You share an IP pool instead. Sending from a shared IP address means that you will send alongside several other Klaviyo customers, which also means a shared sending reputation, as the documentation puts it.
Klaviyo monitors that pool and removes harmful senders from it, but its reputation is not yours to manage. Internalize this early, because it redirects your whole effort. Your domain is the reputation surface you own.
Switching To A Branded Domain Skips Re-Warming After Thirty Days
Two conditions decide whether the move costs you a warm-up. Existing customers moving to a branded sending domain do not have to warm infrastructure again, Klaviyo's documentation states, provided that domain has been registered at least thirty days and already used to send email. Most established senders clear both without noticing.
Genuinely new domains are the exception, where Klaviyo advises starting on a shared sending domain to build reputation first. Established senders gain twice. A branded domain builds your own sending reputation, and it protects you from the effect of other senders on the shared pool.
A DMARC Record Can Exist And Enforce Nothing
Confirming a DMARC record exists is not the same as confirming it works, and this is the step where how to improve email deliverability stops being advice and starts being configuration. Two ways it fails are different from each other, and neither is visible from a casual glance.
p=none Satisfies The Mailbox Providers And Protects Nothing
A DMARC policy of p=none tells receiving providers to take no action on mail that fails authentication. It satisfies the minimum bulk-sender rules ask for while enforcing nothing.
This is the most common false sense of security in the subject. Valimail found awareness of DMARC has reached 78% while enforcement has plateaued at 42%, in its 2026 State of DMARC Report. 25% of domains have DMARC without enforcement.
Valimail attributes that gap directly to the sender requirements. Companies adopted p=none in response to the Microsoft, Yahoo and Google rules without realizing that checking the box for delivery does nothing to protect a domain against misuse. Valimail found marketing and consulting domains fare worst, with 13.73% sitting at p=none with no reporting at all.
Read your own record and look at the policy value. Finding none there means your record only monitors.
A Formatting Error Reads As A Working Record Until A Provider Rejects You
Your second failure mode is more awkward, because a broken record looks present to every casual check. A syntax error only surfaces when a receiving provider parses it. Your first evidence is therefore a rejection.
Exactly that happened to the merchant in Step 2, whose identical campaign delivered nothing to Gmail a week after delivering normally. Verify that your record parses. Confirming it exists proves nothing. That distinction separates a working configuration from a string in your DNS.
Outlook Now Rejects Unauthenticated Bulk Email Rather Than Junking Delivery
Consequences for getting this wrong changed in 2025. Microsoft announced in April of that year that domains sending more than 5,000 emails a day to Outlook.com, Hotmail and Live addresses must pass SPF, DKIM and DMARC. Their stated DMARC minimum is p=none aligned with SPF or DKIM.
That announcement originally routed non-compliant mail to junk. Microsoft revised it before enforcement began in May, deciding to reject those messages outright. They said the change removed confusion for recipient and sender about why a message had been junked.
Microsoft's announcement records what that refusal looks like. The rejected messages will be designated as 550; 5.7.515 Access denied, sending domain [SendingDomain] does not meet the required authentication level. An authentication fault at Microsoft therefore shows up in your bounce log, where a quietly poor open rate once hid it. Finding it got considerably faster.
Volume Changes Trigger Throttling More Reliably Than Volume Itself
Every answer to how to improve email deliverability eventually reaches sending cadence. Mailbox providers watch the shape of your sending more closely than its size, because a brand sending large volume every week is a known quantity to them. A brand that goes quiet for a fortnight and then sends everything in one morning has just become unpredictable.
Pausing Klaviyo Sends Before A Peak Causes The Bounce Spike You Blame On The Peak
Seasonal versions of this cost the most, and they are usually self-inflicted. A Klaviyo Champion and agency partner posting on the Klaviyo Community forum as StefanUE described doing it. His team thought it smart to pause all sends before Black Friday, flows included, then opened the floodgates once their sale started. Result: a sky-high bounce rate on that very first email.
The sudden increase in send volume is the #1 culprit behind BFCM email deliverability issues, by his diagnosis. No fixed threshold defines too much. Any large spike is a flag, and providers throttle until satisfied a sender is legitimate.
Remedying it mid-peak means pulling volume back to normal levels, then ramping up again over several days. That buys room to troubleshoot. Preventing it means ramping volume two to four weeks ahead, with a steady cadence maintained through the run-up.
That same ramping discipline is what a launch sequence is made of. We built the Alma de Ace Coca-Cola collaboration as three phased sends for exactly this reason, and that launch returned 17.4x post-purchase flow revenue. Our piece on how often to send marketing email sets out what steady looks like.
Sending Too Little Damages Reputation As Surely As Sending Too Much
Instinct when deliverability slips is to send less. Klaviyo's documentation warns against treating that as safe. Sending too many emails in a short period can overwhelm customers and produce spam complaints, while sending too few results in lower engagement and a weakened reputation.
Volume reduction is therefore a triage measure buying diagnostic time. It is not a strategy. Left in place, it produces the engagement decline it was meant to avoid.