Sto stands for Send Time Optimization, so send time optimization. It is an intelligent email scheduling feature that helps deliver a message to the right person at the right time—when they are most likely to notice, open, and read the email. Instead of sending a campaign to all contacts at once, Incomaker spreads email delivery throughout the day based on when individual customers typically check their inbox.
Incomaker analyzes the previous behavior of contacts, particularly email opens and past email interactions. Based on this data, it schedules delivery so that each customer receives the email at a time when they are usually active or most likely to engage with their email.
The goal of STO is to increase the likelihood that a customer notices the email at the most appropriate moment. As a result, the feature can help improve campaign open rates.
How STO works
With STO enabled, the campaign does not behave like a one-time mass sending to all contacts at once. The sending is only started at the selected time and the emails are then delivered gradually over the following 24 hours.
For example, if you set a scheduled start for 21. 6. 2026 at 7:05 and you turn on STO, the campaign will start at that time. However, the individual emails will not be sent all at once. Incomaker will spread them out over the course of the day according to the activity of individual contacts.
STO is most beneficial for databases where people read emails at different times. For example, the difference may be more pronounced for contacts spread across multiple time zones. In Europe, where most contacts often travel in one or two time zones, the impact may not be as significant as in the US, for example. Still, STO can help because people have different daily habits and read emails at different times.
Where can STO be set up?
STO settings are configured in the Trigger activity, where all available launch methods are managed. The process is therefore the same for Immediate Start, Repeated Start, and Scheduled Start. Within the settings, simply select the desired launch type in the Trigger activity, enter the required parameters according to the selected mode, and save the settings. This keeps the entire process unified and eliminates the need to describe each launch type separately.
1. Scheduled start
You can enable STO for campaigns that are scheduled to run on a specific day and time.
This includes:
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One-time campaign with a booster
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News notifications
For these campaigns, the sending starts at the selected time and Incomaker then distributes the delivery of emails over the next 24 hours according to the historical activity of individual contacts.
2. Instant start
You can also use STO for campaigns that launch immediately.
This includes:
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Simple one-time campaign
For this campaign, the sending will start immediately after the campaign is launched. If STO is enabled, emails will not be sent to all contacts at once, but will be delivered sequentially over the next 24 hours based on when each recipient is most likely to open.
3. Repeated start
You can also enable STO for campaigns that run repeatedly according to a set rule.
This includes:
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Smart campaign
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Reaching inactive customers
For these campaigns, STO is used on each re-run. Incomaker will always spread out the delivery of emails within a given run so that each contact receives the message at a more appropriate time.
STO is therefore not available for all campaign types, but only where send time optimization provides a practical benefit.
For campaigns such as Pop-up, Holiday, Birthday, Abandoned Cart, or Follow-up After the Event, STO is not used because these campaigns either do not send a traditional mass email newsletter or are tied to a specific event, date, or customer action. Therefore, use STO primarily for campaigns where you want to reach a group of contacts with a marketing email while increasing the likelihood that each recipient receives the message at a more appropriate time.
How to set up STO
STO is activated simply by turning on the switch. STO is activated simply by turning on the STO switch in the Starter activity, the same for all types of starts:
You can enable STO in an activity Scheduled start. You will mainly use this option if you want to start the campaign on a specific day and time.
- Open Smart Flow in which you want to use STO (One-time campaign with re-send, News notification, Simple one-time campaign, Smart campaign, Inactive customer outreach).
- Double-click to open the activity “Scheduled start / Immediate start / Repeated start”.
- At the bottom of the Launcher, you will find “Send Time Optimization (STO)”. Turn on the toggle for this option.
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Continue as you normally would when creating a SmartFlow.
This activates STO. No additional parameters need to be set – the function is simply activated with a switch.
Important to know
After enabling STO, the campaign will not be sent to all contacts at the exact selected time. At the selected time, the sending process only begins, and the system then delivers emails to individual contacts over the next 24 hours based on their historical activity.
For a Scheduled Start, the optimized sending begins from the specific date and time you select. For a Repeated Start, the same principle is applied each time the campaign is triggered.
STO is best used for campaigns where you want to increase the likelihood that contacts receive emails at a more appropriate time. The feature can be enabled in the Scheduled Start or Repeated Start activity within SmartFlow.
Summary
STO is an important feature for smarter and more effective email campaign delivery. It helps ensure that each email is delivered at the time when a specific customer is most likely to notice, open, and read it.
Instead of sending emails to all contacts at once, Incomaker distributes delivery over 24 hours based on the historical activity of individual recipients. As a result, the campaign is better aligned with customer habits and can achieve better results, particularly higher open rates.
STO is especially valuable for campaigns where timing matters. Enabling it is very simple – just activate the Send Time Optimization (STO) switch in the Scheduled Start or Repeated Start activity within SmartFlow. For an Immediate Start, sending begins immediately. When STO is enabled, emails are delivered gradually over 24 hours based on the likelihood of each recipient opening the message.