Smart Sending is a setting on individual Klaviyo emails, SMS, and push messages that skips anyone who already got a marketing message on that same channel within a set window. It's on by default for most campaigns and a lot of pre-built flow messages, and it's easy to leave it there without ever checking whether that's the right call for a specific flow. It usually is. For a handful of flows, it costs you sends you actually wanted to go out.
What does Klaviyo Smart Sending actually do?
At the moment a message is about to send, Klaviyo checks whether that profile already received a marketing message on the same channel inside the Smart Sending window. If they did, the new message is skipped. Not delayed, not queued for later, just skipped. Klaviyo doesn't retry it when the window closes, and the profile doesn't get a makeup send. The person moves on to whatever comes next in the flow (or just never hears about that one campaign) as if the message never existed for them.
That's the part most people get wrong when they first read about it. "Smart Sending" sounds like smart scheduling, like Klaviyo is spacing your emails out intelligently and will still deliver everything eventually. It isn't. It's a frequency cap with no memory. Once a message is skipped, it's gone.
What's the default Smart Sending window?
Straight from Klaviyo's own settings: 16 hours for email, and 24 hours for both SMS and push notifications. Each channel runs its own clock, independently. If you email someone in the morning, Smart Sending on email doesn't stop you from texting them that afternoon. The windows aren't fixed either, you can widen or shrink them per message if the defaults don't fit how often you actually send.
Does Smart Sending affect transactional messages?
No, and this is worth knowing before you worry about it breaking something important. Messages marked transactional in Klaviyo, order confirmations, shipping updates, password resets, are exempt in both directions: Smart Sending never skips them, and receiving one doesn't start a Smart Sending window that could cause a later marketing message to get skipped. Smart Sending only ever looks at marketing sends, campaigns and marketing flow messages, when deciding who to skip.
Which Shopify flows should keep Smart Sending on?
Leave it on wherever the message is informational or promotional rather than tied to a single, time-sensitive action. These flows benefit from the frequency cap doing its job quietly in the background:
| Flow or message type | Smart Sending | Why |
|---|---|---|
| Welcome series | On | Spread across days, no urgency if one send slides |
| Win-back / re-engagement | On | Low-intent recipients, overlap with a recent campaign is a fine trade for not over-emailing someone already drifting away |
| Review request | On | Not time-critical, a skipped request can wait for the next order |
| Newsletter / general campaigns | On (Klaviyo's own default) | You don't want a promo email landing on top of whatever else just went out |
| Replenishment reminders | On | Timed around product usage, not a single narrow moment |
Which flows should you turn Smart Sending off for?
These are the ones built around a narrow, high-intent moment, where a skip means losing the one message that was actually likely to convert:
| Flow or message type | Smart Sending | Why |
|---|---|---|
| Abandoned cart | Off | A shopper who just left checkout is your highest-intent audience that day, don't let an unrelated campaign silently swallow this one |
| Browse abandonment | Off | Same logic, tied to a specific product someone was just looking at |
| Back-in-stock alerts | Off | The shopper asked to be told the moment it's back, a skip means they never find out at all |
| Shipping confirmation follow-ups | Off if marked marketing | Tied to a real event the customer is waiting on; if it's truly transactional it's already exempt |
| Flash sale / price-drop alerts | Off | The entire point is urgency on a specific, short-lived price |
If you're running most of Klaviyo's starter flows, the pattern is simple: anything tied to "this exact thing just happened and they're waiting on it" should skip the skip logic. Everything else can stay on the default.
How do you turn Smart Sending on or off for one message?
Open the message inside the flow or campaign builder, click into its settings in the sidebar, and look for "Skip recently emailed profiles" (the email version; SMS and push have their own equivalent toggle). Check it to turn Smart Sending on, uncheck it to turn it off, and adjust the window length in the same panel if you want something other than the 16 or 24-hour default. It's a per-message setting, not an account-wide switch, so a store can run cart abandonment with it off and the welcome series with it on at the same time.
Because it's set message by message, it's worth actually opening each flow and checking rather than assuming the whole flow follows one setting. Pre-built flows ship with it on for some messages and off for others depending on what the template author decided made sense.
JetFlow generates campaign copy and pushes it into your Klaviyo account rather than sending directly, so once a campaign lands in Klaviyo it's subject to whatever Smart Sending setting is already configured there, same as a campaign you wrote by hand. If open rates on a generated campaign look lower than expected, checking whether a chunk of your list got skipped by an overlapping send is worth doing before assuming the copy or subject line is the problem.
If you're building out flows from scratch and want the fuller build order, our guide to Klaviyo flows for Shopify covers the four to set up first and the filters that keep them from double-sending. For the specific overlap between flows and campaigns on your calendar, this piece on building an email marketing calendar walks through how Smart Sending acts as a backstop there too. And if cart recovery is the flow you're tuning right now, our Klaviyo abandoned cart flow guide and browse abandonment email guide go deeper on the trigger and timing for those specific messages.