The Smart Sending feature allows you to limit the number of emails or SMS messages someone can receive from you in a given period of time. This is a good way to prevent your subscribers and customers from receiving too many messages if you have many active flows and campaigns.
When an email has Smart Sending enabled, Klaviyo will automatically check to see if that recipient has received an email from you within your account's Smart Sending period before it gets sent; it does not check for SMS messages. If this person has received another email from you too recently, the current email to him/her will get skipped. The same is true for SMS Smart Sending; it also won't take recently sent emails into account.
Your email and SMS message Smart Sending windows are configured separately in your account settings.
When a message is skipped due to Smart Sending, it will NOT automatically get rescheduled to send at a later time. This is because we realize most message sends are time-sensitive. If you would like to resend an email that was skipped due to Smart Sending, you must do so manually (through a personal email to one person, or through a campaign for a bulk send).
How to Disable Smart Sending
You can choose to enable/disable Smart Sending on a per-campaign basis. We recommend keeping Smart Sending turned on for most, if not all, marketing emails.
You'll see a checkbox related to enabling/disabling Smart Sending in the first step when you create a campaign.
Change the Smart Sending Timeframe
You can adjust the Smart Sending timeframe for your account by navigating to Account > Settings. To change the timeframe for your SMS messages, head to Settings > SMS and navigate to the SMS Sending Settings section.
For email, if you click into Settings > Email, you will be able to adjust your email Smart Sending period within the Email Conversions & Smart Sending area.
Smart Sending and A/B Testing
A/B tests that receive no results due to Smart Sending are automatically cancelled. This means that everyone in the test pool for your A/B test email campaign got skipped because they received another email too recently. If you receive an in-app notification like the one below, your A/B test has been canceled and you need to resend your campaign to reach your recipients. (A/B testing is not currently available for SMS campaigns.)