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Glossary · E

Email deliverability: what decides the inbox, and the parts you control

It decides whether everything else you've built in email gets seen. Your reports can't see it directly, which is why most shops find out late.

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025Deliverability
The ability of an email to reach the recipient's inbox without being blocked or filtered as spam.
036Email Deliverability
The ability of an email to reach the recipient's inbox without being marked as spam.
A campaign list inside a live client Klaviyo account, each send with the segments it went to, the date it went out and its open and click rates
Not the same as
Delivery. An accepted email can still go straight to spam
Decided by
Each mailbox provider, from your authentication, your reputation and how readers react
Where to look
Google Postmaster Tools, and your clicks split by email domain
Fix first
Authentication on your own sending domain

Delivered means accepted, not inboxed

Here's the awkward bit. When Klaviyo marks an email delivered, the receiving server accepted it. That's all. Where Gmail filed it next is Gmail's business, and it doesn't report back.

What happenedWhat your report showsWhat it means
Refused by the receiving serverA bounceA dead address, or a sender the provider won't take
Accepted, then filed in spamDelivered, then silenceA placement problem the delivered rate hides
Accepted, then sorted into PromotionsDelivered, clicks as normalNothing. That's still the inbox

So a deliverability problem rarely looks like one. It looks like a slow slide in opens and clicks, usually at one mailbox provider first, while the delivered rate sits there looking healthy.

The signals a mailbox provider weighs before your email lands

Look, nobody outside Google knows the exact recipe. The ingredients aren't secret, though. Google's email sender guidelines ask bulk senders to authenticate, offer one-click unsubscribe and keep spam complaints low.

  • Authentication, proving the mail came from your domain through SPF, DKIM and DMARC
  • Reputation, the history your sending domain has built send after send
  • Complaints, or how often readers press the spam button
  • Engagement, meaning whether people open, click, reply or delete without reading
  • List quality, from bounces to old addresses the providers now use as traps

You control the first one today. The rest are earned, slowly, by who you send to and how often.

How to spot deliverability slipping before revenue does

  • Clicks falling at Gmail while Outlook and iCloud hold steady
  • The spam rate creeping up in Google Postmaster Tools
  • Bounces jumping after an import or a big send
  • A send to everyone doing worse per head than a send to your engaged segment
  • Flow revenue sagging with no change to the flows

Any one of those can be noise. Two together, and it's worth pausing the calendar for a day to look.

Where to start when deliverability has already slipped

  1. Set up a branded sending domain in Klaviyo and check the result on a real send
  2. Make an engaged segment the default audience for campaigns
  3. Stop mailing the long-silent with a sunset rule
  4. Keep volume steady, and build it up in steps before peak
  5. Only then look at subject lines, images and links

Most shops want to start at the bottom of that list, because it's the fun end. The fault is almost never there. We've written up why emails end up in spam in the same order, step by step.

Glossary · related

Related terms

DKIMAn email authentication method that allows the receiver to verify that an email was sent and authorised by the owner of the domain.DMARCAn email authentication protocol that helps protect domains from email spoofing and phishing attacks.List hygieneRegularly cleaning your email list by removing invalid or unengaged subscribers to improve deliverability.SpamUnsolicited or irrelevant emails sent in bulk, which can harm sender reputation.Open rateThe percentage of recipients who opened your email, indicating the effectiveness of your subject line and sender name.IP warmingGradually increasing email send volumes to establish a good sender reputation with ISPs when using a new IP address.
How we build email systemsWhat we do inside Klaviyo
FAQs

FAQs

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What's a good deliverability rate for an online shop?

Check which number you're looking at first. Most dashboards only count emails the receiving server accepted, spam folder included, so a perfect-looking rate can hide a lot of junk placement. Judge deliverability on clicks by mailbox provider over time, and on the spam rate Postmaster Tools shows for Gmail.

Is the Gmail Promotions tab bad for deliverability?

No. Promotions is still the inbox, and it's where Gmail expects a shop's marketing to sit. People who want your emails know to look there. Dressing campaigns up as personal notes to sneak into the Primary tab tends to annoy readers once they spot it, and annoyed readers are the ones who complain.

Can anyone guarantee our emails land in the inbox?

No, and run a mile from anyone who says they can. The mailbox provider makes that call on every send, using signals nobody outside it fully sees. What an agency can promise is the groundwork: authentication done properly, a list kept clean, steady volume, and somebody watching the numbers every week.

Not got your answer? Chat to us

Rather we explained it on your own account?

Bring your Klaviyo account to a growth consultation. We'll walk through what this means for your numbers, in plain English, and what we'd fix first.

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Half an hour with Theo, our founder.

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