Send Time Optimization (STO) is an Iterable AI feature that helps send email and push notifications when your contacts are most likely to engage with them. For each recipient of a campaign, STO analyzes historical engagement behavior and selects an optimal, per-person send time.
# In this article
# How Send Time Optimization works
As you use STO, remember that:
STO optimizes send times based on project-specific data. It does not analyze cross-project data for the same contact.
STO is enabled for a single blast campaign and only applies to the campaign you're actively editing.
For predictions, STO considers historical engagement data (such as when users open messages) in order to predict optimal send times.
While STO predictions are made in the user's timezone, STO Insights metrics are reported with all times mapped to the project's time zone for display.
Iterable updates STO machine learning models once per week.
Although STO doesn't guarantee higher engagement, it may improve the Email Open Rate, Email Click Rate, and Push Open Rate campaign metrics.
STO accounts for Apple's Mail Privacy Protection feature.
NOTE
If the STO option isn't available, your Iterable project doesn't have enough engagement data. This is common for staging and test projects. Try switching to a project with more engagement data or wait until your project has built up enough data.
# General send time considerations
STO sends campaigns as described here:
STO is available for both email and mobile push blast and triggered campaigns, email and mobile push send tiles in a journey, and as an email experiment.
Optimized send times always fall at the top of the hour.
When an optimized send time increases through the specified window and peaks after the window ends, STO sends the message at the end of the send time window.
If a user has less than three months of active user engagement data, and Iterable can't determine an optimized send time, messages are sent at the campaign's configured send time (even if STO is enabled).
A rate limit associated with a campaign may cause a campaign to send some messages outside of the STO window.
If you turn on Quiet Hours and STO for a campaign, and the ideal send time for a user falls within your Quiet Hours window, your send won’t be optimized—it will be held until the Quiet Hours window ends. For example, if STO selects 5:00 AM as the ideal send time, but Quiet Hours is set from 9:00 PM to 9:00 AM, the campaign will be sent at 9:00 AM.
If a campaign-triggering API call specifies a specific send time (
sendAt), Iterable doesn't use STO for that send.
# Send time considerations for journeys
The following additional considerations apply for journeys that have STO enabled on an email or push journey tile:
STO sends a message based on the Complete Within value you provide, starting when a user enters the journey. For example, if a user enters a journey at 7:05 a.m. and the send is scheduled to complete within 5 hours, STO will determine the optimal time for the user between 7:05 a.m. and 12:05 p.m.
Disabling a journey that has STO enabled doesn't prevent queued messages from being sent.
If a user satisfies exit criteria in a journey that has STO enabled, the message will still be sent at the optimized time chosen by STO, even though the user exited the journey.
# STO and experimentation
Keep these considerations in mind when using STO with experiments:
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If you're running an experiment with a campaign that also has STO enabled, ensure that the STO window is at least six hours longer than the experiment duration.
For example, you should not specify an STO window of eight hours and an experiment window of three hours.
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You can use STO with or without an STO experiment. Without one, Iterable uses STO for all of the campaign's recipients. With an experiment, STO uses a 50/50 control/variation split for STO experiments. This isn't adjustable.
For more information, see Creating a Send Time Optimization test.
# Send Time Optimization Insights overview
After you've sent messages with Send Time Optimization enabled, you can learn a lot about how your optimized messages are performing by reviewing Send Time Optimization Insights. You can:
Learn about the overall distribution of messages (by percentage or by count) that were sent using optimized send times over time.
Learn about overall engagement for the selected period of time.
View click rate lift and open rate lift metrics to learn how a treatment group (those who received optimized messages) performed when compared to a control group (those who received only unoptimized messages).
View the top and least preferred send windows for messages for the selected period of time.
Learn how many optimized users were sent messages for a given channel (email or push), along with the size of the audience who received optimized sends and the total number of sends.
View details about the volume of messages sent for a given day or time of day.
# Review Send Time Optimization Insights
To review how your message sends are being optimized:
Go to Insights > Intelligent Insights to open the Send Time Optimization Insights page.
At the top of the page, filter message sending optimizations to display data for the past 30, 60, or 90 days. A 30-day view allows you to focus on the impact of a specific campaign, while a 90-day view may help you evaluate how well optimizations are performing more broadly.
From View Trends By, specify whether you want to view data by Percent or by Count.
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In the Send Time Distribution Over Time chart, view how optimized messages were sent for the specified time periods, sorted by weekday and weekend, and also by morning, afternoon, evening, and night.
In Overall Performance, view various lift metrics to learn how a treatment group (those who received optimized messages) performed when compared to a control group (those who received only unoptimized messages).
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In Breakdown by Channel, click the tab for the channel you want to view (email or push). You can view a detailed analysis of lift, engagement, or delivery metrics for optimized sends for the selected channel and message type.
# Want to learn more?
For more information about some of the topics in this article, check out these resources. Iterable Academy is open to everyone — you don't need to be an Iterable customer!
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