Fixing Klaviyo deliverability before it costs you

If you send more than 5,000 emails a day to Gmail, Yahoo or Outlook addresses, you now need to authenticate your domain, offer one-click unsubscribe and keep spam complaints below 0.3%. Miss those and your emails can be rejected outright rather than just landing in spam. Most Klaviyo deliverability problems come from one of those requirements, or from sending to people who stopped opening months ago.

Deliverability problems rarely announce themselves. Open rates slide, flow revenue dips, and it looks like the content got worse when the real problem is that fewer emails reached the inbox.

What do the mailbox providers require?

For senders above roughly 5,000 messages a day, Google, Yahoo and Microsoft now expect:

• SPF and DKIM authentication for your sending domain
• A DMARC record that aligns with your sending domain, set to at least p=none
• One-click unsubscribe in marketing emails, honored quickly
• A spam complaint rate below 0.3%. Google recommends staying below 0.1%, and treats 0.3% as the line you shouldn't cross.

Microsoft has been especially direct about enforcement. Mail to Outlook consumer addresses from high-volume senders that fails these checks can be rejected with a permanent error, so it never reaches the junk folder at all.

How do I check my setup?

Start with three things:

1. A branded sending domain in Klaviyo. Sending from your own domain, with the DNS records Klaviyo provides, builds reputation for your brand instead of a shared one.
2. Your DMARC record. Look up _dmarc.yourdomain.com with any DNS lookup tool. If nothing comes back, you don't have one.
3. Google Postmaster Tools. It's free, and it shows the spam complaint rate Gmail is recording for your domain, which is the number that matters most.

Klaviyo handles the one-click unsubscribe header on its sends, but keep a visible unsubscribe link in every template too. People who can't find the unsubscribe link tend to hit the spam button instead, and that's far more damaging.

Why are my emails going to spam?

The most common causes, roughly in order:

• Sending to unengaged subscribers. When a large share of recipients ignore your emails, mailbox providers take it as a sign people don't want them.
• Sudden volume spikes, like emailing the entire list on Black Friday after months of sending to a fraction of it.
• Complaints from people who forgot signing up, often from old or bought lists.
• Content that looks like spam, such as image-only emails or link shorteners.

How should I segment to protect deliverability?

Send campaigns mainly to people who have engaged recently, then widen carefully. A common starting point is subscribers who have opened or clicked in the last 60 to 90 days.

Be careful with opens, though. Apple Mail Privacy Protection, introduced in 2021, loads emails automatically, so many Apple Mail users register opens they never made. Clicks, site visits and purchases are more reliable signs of engagement.

A sunset flow helps too. It sends a final check-in to people who haven't engaged in a long time, then suppresses those who don't respond. It earns very little directly, but it protects the reputation every other flow depends on. Our breakdown of which Klaviyo flows earn the most puts sunset flows in context.

Should I use double opt-in?

It depends on where your subscribers come from. Double opt-in asks new subscribers to confirm by email, which means fewer sign-ups but almost no fake or mistyped addresses. For sign-up sources that attract a lot of junk, like giveaway forms or aggressive pop-ups, it's worth the trade. For customers signing up at checkout, single opt-in is usually fine.

What if my reputation is already damaged?

Slow down and narrow down. For a few weeks, send only to your most engaged subscribers, fix any authentication gaps, and watch your complaint rate in Postmaster Tools. Once it's healthy, widen your sending gradually rather than jumping back to the full list.

Resist the urge to switch to a new domain to escape the problem. A new domain has no reputation at all, and the habits that damaged the old one will damage the new one just as quickly.

How much can poor deliverability cost?

More than it looks, because the losses hit your best-performing emails first. Flows earn around $1.58 per recipient compared with roughly $0.06 for campaigns. If abandoned cart and welcome emails start landing in spam, that's the revenue you lose, and it rarely shows up as a clear warning in your reports.

Fixing deliverability is part of our Klaviyo email marketing work. At Make Time Wellness, the rebuild started there, because deliverability problems were holding down open rates. If you'd like us to check your sending setup, it's part of our free CRO audit.