Send Time Optimization

Learn more about how to cater a campaign send time for each individual using send time optimization (STO).

Updated over a week ago

Bluecore’s Send Time Optimization (STO) determines the optimal times during a specified time period to send a campaign. Over time, Bluecore’s intelligence optimizes to each individual based on previous open engagement times to individually customize the delivery times of future campaigns. Each send is fully personalized on a per individual basis to reach their personal high-engagement window within a 24-hour period.

Bluecore’s STO analyzes online activity such as clicks and conversions along with several fully-personalized campaigns to determine the best time to reach an individual. Up to three campaigns in a 24-hour day can be sent using STO, while Bluecore decides what times of day and order to be sent it to optimize for site traffic over the day.

STO recommended use cases:

  • Campaigns that are not time-sensitive

  • Large, catch-all audience that’s not specifically segmented or filtered

  • Campaigns that are not promoting low-inventory products



Before adding STO to a campaign, review the STO settings that are available under the email tab of marketing settings.

  1. Navigate to the flag icon on the left-hand side.

  2. Go to Settings.

  3. Click the Email tab.

  4. Then, Send Time Optimization.

A control group is automatically configured to measure the effectiveness of a campaign using STO and cannot be modified. Bluecore automatically holds 50% of the campaign’s audience to serve as a control group for the send. As the model optimizes, it automatically shifts traffic to the test group or back into the control group depending on performance.

The time zone of America/New York is automatically set. If this is not the desired time zone, select a time zone from the drop-down. Bluecore recommends configuring this setting before adding STO to a campaign, as the time zone is used to determine the 24-hour sending window for STO campaigns.


STO is available for daily, weekly, monthly, or one-time automated sends. Add STO to a campaign by selecting Bluecore will decide best send time for each customer when configuring the schedule of a campaign.

Campaigns using STO must be launched before midnight the day of the send for the campaign to send as expected.


STO optimizes for increased clicks in campaign performance, ultimately improving shopper engagement. The STO performance report provides insights into delivers, open rates, click rates, and revenue per email. Access the STO performance report by following the below steps.

  1. Navigate to the chart icon on the left-hand navigation.

  2. Go to Enhanced Analytics.

  3. Then STO Performance Report.

Measure performance of total sends, overall campaign performance, and lift in clicks and conversions.


In order for Bluecore to determine the best send time per customer, we consider the following:

  • For each customer, find an estimate of the value of each hour (probability to click on an email at each hour for that person). We would then have a value function (defined over 24 hours) for each customer that would indicate how valuable sending an email at a certain hour would be for that person. We can get this value function via a regression mechanism on historical data (past delivered times and clicks) and it will be personalized. We may also use other historical data (other online activities) to have a better sense of the customer’s personal online activity times or to group people together and find a common value function for people that “look” alike.

  • From that value function, we can find the best combination of x hours (for x going from 1 to the maximum number of STO campaigns we need to support) to maximize site traffic over the whole day. In order to find those, we also need a function that gives the probability of an email being sent (e.g. not being blocked by any frequency filters) for each time. The x-length tuple of times will be called strategy x.

  • Decide between different length strategies by looking at the customer state when they are eligible at some point in the day to receive an STO campaign. The customer state can be defined by many attributes (total number of campaigns the customer is eligible to receive at that point in time, how late/early it is in the day, how many emails in each strategy are left, etc…). We estimate the value of sending/not sending and make our decision based on that.

Did this answer your question?