Once Send Time Optimization (STO) is enabled for your account, it will appear on the Scheduling page of the eligible email campaigns, and in the Send email node of Automation Center programs.

You turn STO on and off via the toggle switch, and can use it for campaigns launched immediately or those scheduled for a later date.

Once you feel you have launched enough email campaigns, you should start to use STO for all your ad hoc batch campaigns. It will take a number of campaigns before STO has learned enough about the response habits of your customers. Until then, response rates will vary and may even appear to decline. You will be notified on the Send Time Optimization Dashboard widget when the model has become stable enough for the reporting to be statistically relevant. 

For more information, read the Send Time Optimization - FAQ.

When your email campaign is ready to launch, activate Send Time Optimization on the default Scheduling or Advanced Scheduling page. You then have two options:

• Launch now - Emarsys will immediately create a control group comprising 10% of the launch list, and then calculate the optimal sending times for the remaining contacts. Once the calculations are finished, the campaign will be launched to the control group and the first STO launch will take place on the next even or odd hours, depending on your time zone. The remaining contacts will be divided into 11 further launches every two hours.
• Launch control group at - Emarsys will launch the campaign to the control group at the specified time. The 12 STO launches will start and be spread evenly on the calendar day selected for the launch. The time zone of the calendar date is defined on the campaign's Scheduling page.

This feature can currently only be enabled for ad hoc email campaigns.

You can see how the Launch now and Launch control group at options work in the following image:

There are some differences in behavior for STO depending on whether you are using simple or advanced scheduling.

When using Advanced Scheduling:

• If you are using A/B testing, STO will only be enabled for the final mailing. All the versions you use to test will be launched as normal emails. 

• It is not currently possible to abort the STO launches. You can, however, unschedule a scheduled launch when there are at least 30 minutes left until the launch. If it is still critical to abort the STO launch, contact Emarsys Support to abort your emails.
• The launches are started on the scheduled day at the time defined in the launch schedule. If you want to ensure that the launches are all sent on the same calendar day, you must set a launch schedule time of 00:00.

You can also enable STO for batch email nodes in any program that does not start with a transactional entry node (i.e. not Form, Data Change or New Contact).

The behavior is the same as for ad hoc batch emails:

• A 10% control group is automatically created and launched as soon as the email is triggered.
• The remaining 90% of contacts will be split up in 12 launches over the following 24 hours.
• The responses will show up on the STO widget.

Additionally, the following behavior should be noted:

• Pausing or aborting a program will not stop STO emails that are already scheduled for launch. If it is still critical to abort the STO launch, contact Emarsys Support to abort your emails.
• Launches smaller than 100 contacts will not be counted on the STO widget (as there will be no control group).
• When an AC program sends out a campaign using STO, the next node will only be processed when all mail has been sent out, which means that an STO node will always take 24 hours to process.

STO needs to calculate the launch time for every contact in your launch list. When sending your first campaign, you should allow at least two hours for the initial calculations.  

For subsequent campaigns, the time it takes for STO to calculate the best sending times may range from a few minutes to two hours. The actual calculation time depends on the size of your database as well as the complexity of the contact segment and the launch list.