- Klaviyo Smart Sending skips a marketing message if the person already got one on the same channel inside the window: 16 hours for email, 24 hours for SMS and push by default.
- Skipped means gone. Klaviyo does not reschedule it. Your abandoned cart email can vanish because a campaign went out 3 hours earlier.
- It only touches marketing messages. Transactional emails are never skipped and never start the timer.
- Turning it off on one message resets the timer for everyone it was sent to. That can knock out your next campaign.
- Plan your weekly send count first with the email frequency planner, then use Smart Sending as the safety net, not the plan.
Klaviyo Smart Sending is one checkbox most Shopify stores never think about. It sits on by default, quietly skipping emails so nobody gets hammered. Great idea. But it also decides, without telling you, that some of your most valuable flow emails don’t go out at all.
An abandoned cart flow with “low volume” is often nothing more than a daily campaign plus a 16-hour Smart Sending window. Nothing is broken. The setting is doing exactly what Klaviyo’s help docs say it does.
So here’s Klaviyo Smart Sending explained the practical way: the rules, the traps, and the setup I’d use for a Shopify store.
Email Send Frequency PlannerBefore you touch Smart Sending, find the weekly send count that earns the most without burning your list.Run my numbers →Klaviyo Smart Sending explained in 60 seconds
Think of it as a countdown timer on every profile. When Klaviyo tries to deliver a marketing message to someone, their timer starts for that channel. Until it runs out, any other marketing message on that channel with Smart Sending switched on skips them.
| Channel | Default window | Blocks |
|---|---|---|
| 16 hours | Other marketing emails only | |
| SMS | 24 hours (separate campaign and flow settings) | Other marketing SMS only |
| Push | 24 hours (separate campaign and flow settings) | Other marketing push only |
Five rules from Klaviyo’s documentation that matter more than anything else:
- Skipped is final. Messages skipped due to Smart Sending are not rescheduled automatically.
- Channels don’t talk to each other. An email doesn’t block an SMS. You can send both on the same day.
- Transactional is exempt. Order confirmations and other transactional messages are never skipped and never start the timer.
- Failed sends still count. The timer starts for everyone Klaviyo tries to deliver to, including bounces and messages filtered by the inbox provider. People Klaviyo skipped (by Smart Sending, filters or exclusions) don’t start a new timer.
- It’s on by default for campaigns and in many pre-built flows. Klaviyo recommends keeping it on for most marketing emails.
7 Smart Sending tricks most stores miss
1. Your flow emails are the ones getting skipped
Campaigns go out at a time you choose. Flows fire whenever someone acts. So if you send a campaign every morning, a big slice of your list is inside a 16-hour window most of the day, and every cart, browse or back-in-stock email with Smart Sending on has to dodge it. The cheapest, highest-intent emails you have lose to a broadcast.
2. Switch it off on your highest-intent flow emails
My default for Shopify stores: Smart Sending off on abandoned checkout email 1, and usually on back-in-stock alerts. Someone who just left a full cart wants that email more than your Tuesday newsletter. In a flow, the setting is Skip recently emailed profiles under each email’s settings. This is my judgement call, not a Klaviyo rule, so test it against your unsubscribe rate.
3. Keep it on for anything triggered by repeat behaviour
Klaviyo’s flow troubleshooting guide says to keep Smart Sending on for flows triggered by behaviour people repeat, like viewing a product or being active on site. One person can view 12 products in a session. Without it, your browse abandonment flow can stack emails fast.
4. Turning it off resets the clock
This one surprises people. When you send a marketing email with Smart Sending off, the timer resets to the full window for everyone Klaviyo attempts to deliver it to. So a cart email at 9 pm with Smart Sending off can block tomorrow morning’s 10 am campaign for that shopper. Usually fine. Just know it’s happening.
5. Change the window before the first send, not after
Window changes aren’t retroactive. Klaviyo’s example: send a campaign with a 5-day window, change it to 1 hour, and the next Smart Sending email is still skipped until the full 5 days pass. Planning a two-send day for a big sale? Shorten the window before the first email goes out. Or send the second one with Smart Sending off.
6. Don’t let it eat your A/B tests
If everyone in an A/B test pool gets skipped because they were emailed too recently, Klaviyo cancels the test automatically. Klaviyo’s Academy also lists running several A/B tests without over-sending as a reason to keep it on. Space test sends and check you have enough people left, using my guide to Klaviyo A/B test sample size.
7. Build your own cross-channel rule
Because email never blocks SMS, a shopper can get a campaign email, a campaign text and a cart text inside a few hours. Smart Sending won’t stop that. Add a filter on SMS steps for people who received an email recently, or simply schedule texts well away from email sends. Texts cost money every send, so this also protects your SMS ROI.
Which messages should have Smart Sending on or off?
My starting point for a Shopify + Klaviyo account. Adjust once you see the skip numbers.
| Message | Smart Sending | Why |
|---|---|---|
| Regular campaigns | On | Klaviyo recommends it for most marketing email; stops double sends |
| Abandoned checkout email 1 | Off | Highest intent; a skip is lost revenue, not rescheduled |
| Abandoned checkout emails 2–3 | On | Lower urgency, fine to defer to Smart Sending |
| Browse abandonment / site activity | On | Repeat-trigger behaviour, Klaviyo says keep it on |
| Back in stock alert | Off | They asked for it, and stock may sell out |
| Welcome email 1 | Off | They just signed up and expect it now |
| Post-purchase cross-sell, win-back, sunset | On | Not time-critical |
| Order and shipping confirmations | Not affected | Transactional messages are never skipped |
Worked examples
A Shopify store sends a campaign to its engaged segment at 10 am every day. With a 16-hour email window, anyone who got it is blocked until 2 am the next morning.
- A shopper on that segment abandons checkout at 1 pm. Cart email 1 is set to wait 4 hours, so it fires at 5 pm.
- Smart Sending is on: the email is skipped. It is not sent later.
- Cart email 2 fires the next day at 1 pm, after that morning’s campaign: skipped again.
- Say 300 checkouts a month come from people on that daily segment. If even a third hit an open window, that’s 100 cart emails a month that never left Klaviyo. Switch email 1 to Smart Sending off and they go out.
A brand plans a launch email at 9 am and a “last hours” reminder at 7 pm to non-buyers. That’s 10 hours apart, inside the 16-hour default.
- With Smart Sending on for both, the 7 pm reminder skips everyone who got the 9 am email. Most of the list sees nothing.
- Fix A: turn Smart Sending off on the reminder only, and exclude buyers and unengaged profiles so you’re not hitting cold contacts twice.
- Fix B: shorten the email window to 8 hours before 9 am. Changing it at noon would be too late for the morning recipients.
How to change your Smart Sending settings
- Email window: click your organization name (bottom left), then Settings > Email > Sender preferences, and change the Smart Sending Period in hours.
- SMS and push windows: same place under SMS or Push notifications. Each has a separate window for Campaigns and Flows.
- One campaign: in the campaign’s settings (or the Recipients step in the simple wizard), switch off Turn on Smart Sending. For SMS you can keep just one check: skip people who got a campaign message, or skip people who got a flow message.
- One flow message: click the message and clear Skip recently emailed profiles (email) or switch off Smart Sending (SMS, push).
A small SMS gotcha: SMS Smart Sending works on the phone number. If several profiles share one number, a text to one can skip the others.
Smart Sending is a safety net, not a send schedule
Here’s the mindset shift. Smart Sending doesn’t decide how often you should email. It just stops two emails landing too close together. If half your sends get skipped, you’re planning too many, or planning them badly.
Work it the other way round:
- Pick a weekly campaign count that balances revenue and unsubscribes. That’s exactly what the email frequency planner models.
- Send more to engaged people, less to quiet ones. Fewer sends to cold profiles also helps deliverability, see my Gmail and Yahoo sender requirements guide, and check rates with the unsubscribe rate calculator.
- Protect the money flows. Decide which flow emails must always send, and switch Smart Sending off on just those.
- Prune who’s left. People who never open shouldn’t be in the window race at all. A Klaviyo sunset flow handles that and can also lower your Klaviyo bill.
Then check your abandoned cart flow numbers a month later. If recipients went up while orders per recipient held, Smart Sending was costing you money. Put the extra recovered carts into the abandoned cart calculator to see the yearly figure.
Want Inboxoo to set this up for you?
We build and run Klaviyo email & SMS retention for Shopify brands and get paid on results.
Chat on WhatsAppWant to know the exact quotation? Contact now
FAQ
What is Smart Sending in Klaviyo?
Smart Sending is a setting that skips a marketing email, SMS or push notification if the recipient already received a message on the same channel within a set window. The defaults are 16 hours for email and 24 hours for SMS and push. Each channel has its own window.
Are emails skipped by Smart Sending sent later?
No. Klaviyo’s help docs say messages skipped due to Smart Sending are not rescheduled automatically. You can resend a skipped email campaign, but SMS and push can only be resent manually.
Does Smart Sending apply to transactional emails?
No. Smart Sending only applies to marketing messages. Messages marked as transactional are never skipped, and receiving one does not cause the recipient to be skipped from later messages.
Does an email block an SMS under Smart Sending?
No. Email, SMS and push have separate windows and are managed independently, so someone can get an email and an SMS from you on the same day with Smart Sending on.
How do I change the Smart Sending window in Klaviyo?
For email, go to Settings, then Email, then Sender preferences, and change the Smart Sending Period in hours. SMS and push have their own settings with separate windows for campaigns and flows. A change only applies to new countdowns; people already inside a window keep the old duration.
Should I turn off Smart Sending on my abandoned cart flow?
It is a judgment call. If you send campaigns most days, Smart Sending can skip a large share of cart emails, and they are not rescheduled. Many brands switch it off on the first cart email and keep it on for later steps. Remember that turning it off resets the timer for everyone who gets that email.
Why was my Klaviyo A/B test cancelled?
If everyone in the test pool was skipped because they received another message too recently, Klaviyo automatically cancels the A/B test. Resend the campaign to reach those recipients, or space your sends further apart.
Want Inboxoo to set this up for you?
We build and run Klaviyo email & SMS retention for Shopify brands and get paid on results.
Chat on WhatsAppWant to know the exact quotation? Contact now
Keep reading
The Klaviyo abandoned cart flow setup
Trigger, filters, timing and discount rules for a cart flow that recovers revenue without training buyers to wait for a code.
7 min read →Klaviyo flowsThe Klaviyo browse abandonment flow
Trigger, filters, timing and a 2-email structure for the flow that catches window shoppers before they buy elsewhere.
8 min read →TestingKlaviyo A/B test sample size
Klaviyo’s own significance thresholds, the sample size formula, a cheat sheet and fixes for small lists.
8 min read →- Klaviyo Help Center: Understanding Smart Sending in Klaviyo
- Klaviyo Help Center: Troubleshooting why a profile is scheduled in a flow multiple times
- Klaviyo Academy: Use Klaviyo’s sending features
Worked examples in this post use illustrative numbers, not client results. Benchmarks are linked to their original publisher.