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TL;DR: Klaviyo emails go to spam for one of nine reasons, and almost all of them trace back to sender reputation, not spam words. Since 2024, Gmail and Yahoo require every bulk sender to authenticate with SPF, DKIM, and DMARC, offer one-click unsubscribe, and keep spam complaints under 0.3%. Fix the technical setup, then email only engaged subscribers and clean your list on a schedule. Do both and inbox placement recovers within a few weeks.
Klaviyo emails go to spam when your sender reputation, authentication, or list engagement fails the rules Gmail and Yahoo enforce on every bulk sender. Since February 2024, both providers filter or reject mail that isn't authenticated, doesn't offer one-click unsubscribe, or draws too many spam complaints. Microsoft's Outlook added the same rules in May 2025.
Here's the part most guides skip. Spam placement is roughly 80% sender reputation and engagement, and only a small slice is content. Swapping a few "spam words" won't save you. What matters is whether real people open your mail and whether the mailbox providers trust your domain.
The good news is that this is fixable, usually within a few weeks. Below are the nine reasons Klaviyo emails land in spam and the exact fix for each, in the order that moves the needle fastest. Across the Shopify stores we manage at CartStrings, tightening these levers is what takes a brand from the promotions tab to a 99.8% inbox delivery rate.
Why do emails hit spam?
Emails hit spam when mailbox providers don't trust the sender. Sender reputation and subscriber engagement drive roughly 80% of that decision. Authentication, complaint rate, and content fill the rest. Fix reputation and engagement first, because no clever subject line outruns a domain Gmail has learned to distrust.
Reputation is a score Gmail, Yahoo, and Outlook assign to your sending domain and IP. They build it from how recipients treat your mail. Opens and clicks lift it. Deletes without opens, spam complaints, and hits to dead addresses drag it down. The frustrating part is that reputation is sticky. One bad send can shadow your next month of campaigns. That's why the brands with the cleanest inboxes treat deliverability as an ongoing habit, not a one-time fix. If you want a second set of eyes on where your score is leaking, that's the core of our email deliverability work.
Is your email authenticated?
Authentication proves you own the domain you send from. Gmail and Yahoo require three records: SPF, DKIM, and DMARC. Miss any one and bulk mail goes straight to spam or gets rejected outright. Set all three in your DNS, then confirm they pass inside Klaviyo before your next send.
SPF names the servers allowed to send for your domain. DKIM adds a cryptographic signature so providers can confirm the mail wasn't tampered with. DMARC ties the two together and tells inboxes what to do when a message fails, with a policy of at least p=none required. If you send 5,000 or more emails a day to Gmail or Yahoo, these aren't suggestions anymore, they are hard requirements. Klaviyo walks through the exact DNS setup in its sender requirements guide, and a quick Klaviyo audit will flag any record that isn't aligned.
Use a branded domain
By default, Klaviyo sends your email from a shared domain, which means your reputation is pooled with every other brand on that infrastructure. If one of them sends junk, your inbox placement takes the hit. A branded sending domain, sometimes called a dedicated domain, isolates your reputation so only your own sending habits shape it.
Two rules go with this. First, never send from an @gmail.com or @yahoo.com address. Those fail domain alignment and get filtered instantly. Use an address on a domain you own. Second, when you set up a new branded domain, warm it slowly. Start by sending to your most engaged subscribers and ramp volume over a couple of weeks so the providers learn to trust you. Jumping straight to a full-list blast on a cold domain is one of the fastest ways to earn a spam label.
Who are you emailing?
This is the reason most brands miss. Emailing people who never open teaches Gmail your mail is unwanted, and that reputation hit follows every future send. One blast to a stale list can bury your next month of campaigns in the spam folder.
It becomes a spiral. You send to unengaged contacts, your open rate drops, the providers read that as a signal your mail is unwanted, so more of it gets filtered, which pushes engagement even lower. The way out is to change who you email. Build engaged segments, people who opened or clicked in the last 30 to 90 days, and send your campaigns there first. Expand to colder segments slowly and only when your reputation is healthy. This is also why automated flows outperform one-off blasts. Klaviyo's benchmark data shows flows drive roughly three times the click rate of campaigns, because they fire when someone is actually engaged. Get the targeting right in your email campaigns and half the deliverability battle is already won.
Here's a simple test. Pull your open rate on your last full-list campaign, then pull it on a campaign sent only to 30-day openers. If the gap is wide, your list is the problem, not your subject lines. Klaviyo's benchmark data puts a healthy promotional open rate near 38%, so if your blasts sit far below that, you're almost certainly dragging along a large block of contacts who will never open again. Trimming them feels like shrinking your reach, but it's the opposite. You reach more real people because more of your mail actually lands.
What's a safe complaint rate?
Keep spam complaints under 0.1%, which is one complaint per 1,000 emails. Gmail starts throttling you above that, and 0.3% is the hard limit where sends get blocked. The fastest way to lower complaints is a visible, easy unsubscribe, which Gmail and Yahoo now require anyway.
People mark mail as spam when they can't quickly find the exit. Klaviyo adds a one-click unsubscribe link to the header of every email automatically, but you should also keep a clear unsubscribe link in the body. Counterintuitive as it sounds, making it easy to leave protects your reputation far more than hiding the link ever could. Watch your complaint rate in Klaviyo's deliverability tab after every campaign, and if it creeps toward 0.3%, pull back on frequency and tighten your segments before it turns into a block.
Clean your list often
Dead addresses and chronic non-openers are dead weight. They lift your bounce rate, drag your reputation down, and give the mailbox providers a reason to distrust you. Cleaning your list on a schedule keeps only the people who actually want your mail, which is exactly what deliverability rewards.
Suppress hard bounces immediately. For subscribers who've gone quiet, run a sunset flow: a short series that asks for one last click, then suppresses anyone who doesn't respond. Yet most brands never do this. Industry surveys show only about a quarter of senders have any sunset policy at all, which is a big reason so many sit in spam. A monthly cleanup is a reasonable cadence for most Shopify stores. Setting up a proper sunset sequence is a standard part of our email automations builds, and our full list cleaning guide walks through the segments step by step.
Does your content look spammy?
Content is the smallest lever, but it still matters. All-image emails with no live text are the classic trap, since filters can't read them and screen readers can't either. Aim for roughly 60% text to 40% images, host images on a domain you control, and skip obvious triggers like "FREE MONEY" in all caps.
A few more content habits quietly hurt placement: broken links, link shorteners that look like phishing, misleading subject lines that don't match the body, and sending from a no-reply address that fails alignment. Fix those and your content stops working against you. And keep junk off the list in the first place with a clean opt-in. A well-built capture form, rather than a bought or scraped list, is the foundation everything else sits on, which is why we treat popups and capture as a deliverability issue, not just a growth one.
Fixing it for good
Klaviyo emails going to spam almost always comes down to two things: a domain the mailbox providers don't trust, and a list full of people who stopped caring. Fix authentication and your sending domain first, because those are one-time setups. Then change who you email. Send to engaged subscribers, clean your list on a schedule, and keep complaints under 0.1%. Do that and inbox placement recovers within a few weeks.
If you'd rather not guess your way through DNS records and segment logic, that's what we do all day. A Klaviyo audit shows exactly where your deliverability is leaking, and our deliverability service fixes it. Book a call and we'll take a look at your account.
Frequently Asked Questions
Why suddenly going to spam?
A sudden drop usually means your sender reputation took a hit. The most common cause is a campaign sent to a stale or unengaged list, which spikes your complaint and bounce rates. Check your recent sends in Klaviyo's deliverability tab for a jump in complaints or bounces, then pause and rebuild your engaged segments before sending again.
How do I stop it?
Work in this order: authenticate your domain with SPF, DKIM, and DMARC, move to a branded sending domain, email only subscribers who engaged in the last 30 to 90 days, keep spam complaints under 0.1%, and clean your list monthly. The technical fixes are one-time, but the list habits are what keep you in the inbox long term.
Does a dedicated domain help?
Yes, a branded or dedicated sending domain isolates your reputation so other senders can't drag it down. But it only helps if you pair it with good list habits. A dedicated domain sending to an unengaged list will still land in spam, because reputation is built from engagement, not just infrastructure.
What's a good complaint rate?
Keep it under 0.1%, which is one spam complaint per 1,000 emails. Gmail recommends staying below that, and 0.3% is the hard threshold where your sends can get blocked. A clear, easy unsubscribe link is the simplest way to keep complaints low, since frustrated readers hit "spam" when they can't find the exit.
How long to fix it?
Most brands see inbox placement recover within a few weeks of consistent sending to engaged subscribers. Warming a brand-new sending domain can take longer, sometimes a month or more, because the mailbox providers need time to build trust. There's no instant fix, but steady, engaged sending gets you there reliably.
