When Dermavenue joined us in March 2026, it had decent traffic and a solid list, but its emails weren't reliably reaching people.
After we fixed the deliverability issues, campaigns sent to 560,040 recipients between April and June averaged a 59.09% open rate, and Klaviyo revenue grew 2,691% to $398,191.56 in about nine weeks.
Deliverability affects plenty of important metrics. So, there's little point improving your subject lines or building new flows if a significant share of your emails are landing in spam.
What email deliverability actually is
Deliverability refers to the share of your emails that reach the inbox, as opposed to bouncing, getting blocked, landing in spam or getting sent to Gmail's Promotions tab.
Mailbox providers like Gmail decide where your email goes mostly based on how people treat it. Opens and clicks improve your sender reputation. Deletes, ignores, bounces and spam complaints bring it down.
That's why deliverability problems so often get mistaken for copy problems. When open rates fall, someone rewrites the subject lines, nothing changes, and the real cause often goes unnoticed. Our guide on why emails land in Promotions and how to fix it covers that issue in depth, and I made a video on the fix that actually works in 2026.
The numbers we work to
Google's bulk sender rules require keeping your spam complaint rate below 0.3%, and the safe target is under 0.1%. We aim well below both.
Here's what that looks like in a real, high-volume account. In one week of October 2026, Michael Gabriels sent emails to more than 128,000 recipients across its five biggest inbox providers:
| Metric | That week | Week before |
|---|---|---|
| Bounce rate | 0.12% | 0.23% |
| Spam complaint rate | 0.02% | 0.013% |
That spam rate is a fifth of Google's 0.1% safe target, and the bounce rate went down by nearly 50% compared to the week before. We report these numbers to the client every week, alongside revenue, so problems get caught before they cost money.
How we diagnose a deliverability problem
Check the setup. Is the sending domain configured properly in Klaviyo, with authentication and tracking working? It's unglamorous, and it's surprising how often it's broken. My walkthrough on setting up a branded sending domain in Klaviyo covers this step.
Then the list. Look at bounce rates, unsubscribes, and how long people have been inactive. A list full of people who haven't opened in a year is a liability, not an asset.
Segment by engagement. Recently engaged subscribers get sent to first. People who've gone quiet get separated into their own segment.
Suppress and sunset. If someone is never going to open, stop paying to email them so they don't drag down everyone else's inbox placement.
Rebuild volume slowly. Send to the engaged core to let your reputation recover. Then, widen the audience as opens and clicks improve.
I show the full review process in how to review deliverability in Klaviyo, and it's the first thing we check in any account we take on.
Sunsetting pays for itself
Suppressing inactive subscribers protects deliverability and saves money.
For example, in September 2026, we ran a last-chance re-engagement campaign for Michael Gabriels before suppressing its inactive profiles. It won back 420 people and about $1,000 in revenue.
Then we suppressed roughly 9,000 profiles that still weren't engaging, after checking that no buyers were among them. That stopped the brand's Klaviyo bill from rising from $1,205 to $1,275, and set them on course to $1,115.
I cover this approach in a Klaviyo strategy to lower your bill.
What fixing it looked like in real accounts
| Client | What we did | Result |
|---|---|---|
| Dermavenue | Fixed deliverability alongside the flow build, with sunset and suppression from day one | 59.09% campaign open rate across 560,040 recipients, and Klaviyo revenue up 2,691% |
| Metalbird | Ran seven Klaviyo accounts in seven markets as one consistent system | Open rate increased from 44.9% to 51.6% |
| Skinny Fizz | Cleaned up deliverability and list health so volume could grow safely | Email revenue up 921% in 30 days |
| Michael Gabriels | Engagement scoring, weekly monitoring and regular sunsetting | 57% open rate across the peak-season programme, with spam complaints around 0.013% |
Where deliverability meets your flows
Automated flows keep sending even when you're not running campaigns, so they're where deliverability problems show up first. A welcome flow firing at an unengaged list damages the sender reputation that every campaign after that relies on. That's why we put suppression rules in place before building flows, and why we vet the people who build them.
Our guide on how we hire and test Klaviyo email builders explains that process.
Rendering matters too. Broken layouts on mobile get deleted, and deletes count against you. Our guide on testing emails across multiple devices shows how to check, and our free email templates are built to render cleanly across inboxes.
A quick deliverability checklist
- Branded sending domain and authentication set up in Klaviyo
- Spam complaint rate under 0.1%, and never near Google's 0.3% limit
- Bounce rate tracked weekly against your own baseline
- Engaged subscribers identified and sent to first
- Inactive subscribers given one last re-engagement campaign, then suppressed
- Test sends checked across a range of inboxes, including Gmail's tabs
Not sure if you have a problem?
If your open rates have fallen and you can't work out why, start with the checklist above and look at your engaged segment first. Our bad email marketing examples show the habits that hurt inbox placement, and our ecommerce email marketing case studies show what recovery looks like in real accounts.
Figures come from In-box client accounts and published case studies. Results depend on each account's starting point, list and market.
