Smart Sending in Klaviyo: Set Your Sending Frequency Before BFCM

During Black Friday and Cyber Monday, a store sends more campaigns than usual while its flows keep running. Smart Sending is the Klaviyo setting that decides, for each profile, whether a new marketing message goes out or is skipped because another message was sent too recently. Misunderstood, it makes part of your list miss a send on the very day you are counting on it.

TL;DR. The default window is 16 hours for email, 24 hours for SMS and 24 hours for push. A window change does not apply retroactively. A message skipped by Smart Sending is not rescheduled automatically. According to the Smart Sending page, transactional messages are never skipped (an account setting can nonetheless apply Smart Sending to them). In our view, the window should be set and checked several days before the event, not on Friday morning.

Want an outside look before you build? We offer a Q4 readiness audit: 30 minutes, free, no strings attached.

What Smart Sending does

Smart Sending limits the number of emails, SMS or push notifications a person can receive over a given period. Klaviyo's documentation presents it as a way to keep a subscriber from receiving too many messages at once when many flows and campaigns are active (Klaviyo, understanding Smart Sending).

A few basic rules to keep in mind:

• Each channel has its own window: 16 hours by default for email, 24 hours for SMS, 24 hours for push.
• Channels are handled separately. After an email, an SMS can go out the same day with Smart Sending turned on.
• Smart Sending only applies to marketing messages. According to the Smart Sending page, transactional messages are never skipped, and receiving one does not cause the recipient to be skipped afterwards. The account default settings page nonetheless says a setting lets you choose whether Smart Sending applies to transactional emails sent with Klaviyo: check it in your account.
• If Smart Sending is turned off for a message, the recipient can receive it even if the window has not ended.
• Skipped messages are not rescheduled automatically.

To resend an email to skipped people, the page points to a dedicated resend procedure in Klaviyo. For an SMS or a push, the documentation states that it is not possible to resend the message to skipped people other than by hand.

The timer: how Klaviyo decides to skip a profile

The page describes Smart Sending as a countdown attached to each profile. Its length is the window in force at the time of sending. The countdown starts for everyone Klaviyo attempted to deliver the marketing message to: those who received it, and those for whom the send failed after leaving Klaviyo, for example a bounce or filtering by the mailbox provider. It does not start for people Klaviyo skipped, whether because of Smart Sending, a flow filter, or an excluded list or segment (Klaviyo, understanding Smart Sending).

Two consequences follow from this mechanic.

A window change is not immediate. One example from the page: you send an email to the whole list, then change the window from 5 days to 1 hour, then send a second email with Smart Sending. That second email is skipped, and so are all emails with Smart Sending sent in the following 5 days, because each profile's timer was set with the old length. The same principle applies to our case: if you shorten the window from 16 to 10 hours right after a campaign, that campaign's recipients stay skipped until the 16 hours are over.

Only a send without Smart Sending refreshes the timer. When you turn off Smart Sending for a message, Klaviyo sends it to everyone, and because it attempts a new delivery, the timer is reset to the window in force. The page covers the case of groups: if a profile did not receive that message without Smart Sending, for example because it was not part of the targeted segment, its timer is not reset and it stays skipped for longer. This is the only documented way to change a profile's timer.

Where to set the window

For email, the page indicates: organization name at the bottom left, Settings, Email, Sending preferences, then the number of hours under Smart Sending Period. For SMS, the path goes through SMS, Sending preferences, and you can set separate durations for campaigns and for flows. For push, go to Settings, Push notifications, then click Update Push Sending Settings after making the change (Klaviyo, understanding Smart Sending).

For SMS, one detail deserves attention: Smart Sending is based on the phone number. If several profiles share the same number and that number received an SMS within the window, new messages to that number are skipped, whichever profile triggers the send.

Campaigns: on by default, can be turned off case by case

In campaigns, Smart Sending is on by default. You can turn it off for a specific campaign at step 1, by unchecking the option that skips profiles who recently received an email. Klaviyo recommends keeping it on for most, if not all, marketing emails. For SMS, there are two checkboxes: skip profiles who recently received a campaign message, and skip those who recently received a flow message. For push, an equivalent checkbox exists.

What to do with sends close together

BFCM puts this rule to the test: the morning send and the evening send sometimes fall less than 16 hours apart. Here are three options, in our view, in order of caution.

The second choice assumes you changed the window before the first sends of the event, so that timers already running do not keep the old length. This is why we advise deciding on the window in the week before, with the BFCM send calendar in front of you. Preparing audiences and exclusions completes this choice, since segment exclusions also cause profiles to be skipped.

Flows: one setting per message

In flows, the documentation does not give a single rule. The Smart Sending page states that Smart Sending is on in many prebuilt flows, with the option to turn it off message by message. The flow frequency page states that flow messages do not have Smart Sending on by default, and that you can turn it on for a specific message by checking Skip recently emailed profiles in the message settings (Klaviyo, optimizing flow sending frequency). A third page, on account default settings, states that Smart Sending is on by default for all flow emails, except prebuilt abandoned cart emails (Klaviyo, understanding account default settings). These three statements do not agree with each other, and we cannot settle it from the documentation: open each message rather than assuming.

Our advice, in our view: before BFCM, go through your abandoned cart, browse abandonment and post-purchase flows, and note for each message whether the box is checked. An abandoned cart email skipped because the customer received a campaign two hours earlier is a case to decide consciously before the event and to avoid discovering afterwards. For cart reminders, the guide to abandonment flows covers the delays.

Recommended flow frequencies

The flow frequency page gives a table of recommended frequencies, based on what Klaviyo observes across the average brand. Here are the delays the table associates with each type of flow:

• Welcome series: immediately, then 4 days.
• Abandoned cart: 4 hours, then 1 day.
• Browse abandonment: 2 hours.
• Post-purchase: immediately, then 3 days, then 1 week.
• Winback: 2 months, then 3 months.
• Anniversary: 1 year.
• Sunset: 1 day, then 1 week, then 2 weeks.

The page specifies that the optimal frequency varies from one business to another and that this is a starting point.

To find the right delay, the frequency page suggests a test with a conditional split: you choose Random sample as the condition, set the share of the audience that takes the "yes" branch (50% for a balanced test), place different delays on each branch and duplicate the email so the content is identical. The page specifies reconnecting the "no" branch to the "yes" branch after the first email if the flow contains others. Our guide to A/B testing in Klaviyo details how to read the results.

Smart Sending and campaign A/B tests

A campaign A/B test whose test group recipients were all skipped by Smart Sending is cancelled automatically, with an in-app notification. You then need to resend the campaign to reach the recipients (Klaviyo, understanding Smart Sending). A typical case, in our view: a subject line test launched on a segment that has just received another message. Our article on BFCM email subject lines presents the testing method.

Checklist before BFCM

These points are Deliver advice.

1. The email, SMS and push windows are reviewed in the settings, and the value is known to the whole team.
2. Any window change is made several days before the first sends of the event.
3. For each campaign in the calendar, the Smart Sending box is checked or unchecked on purpose.
4. The messages of critical flows have been opened one by one to check the Skip recently emailed profiles box.
5. Segments that must receive two sends on the same day are identified in advance.
6. An A/B test is not launched on a segment that has just received another message.

FAQ

What is the default Smart Sending window?

16 hours for email, 24 hours for SMS and 24 hours for push.

Is a message skipped by Smart Sending sent again later?

No. Skipped messages are not rescheduled automatically. For an email, a resend procedure exists. For an SMS or a push, the resend is done by hand.

Does Smart Sending block a transactional email?

No, according to the Smart Sending page: transactional messages are never skipped, and they do not cause later marketing messages to be skipped either. An account setting (Settings, Email, Sending preferences) does let you choose whether Smart Sending applies to transactional emails sent with Klaviyo.

Did an email block an SMS for me?

No. The windows of each channel are independent.

Can I shorten the window on the same day?

The change is not retroactive: profiles already served keep the timer set with the old length. A message sent without Smart Sending resets it for the profiles that received it.

Want an outside look at your sending settings? We run Q4 readiness audits, or you can talk directly with the Deliver team.