Send Time Optimization (STO) is a feature that uses an algorithm to find the best time to send the campaign to the subscribers in the next 24 hours based on their engagement history.
This article explains the following:
Why do we need STO?
STO enables you to adapt your campaigns to the individual usage patterns of your subscribers. Your emails will be more likely to show up at the top of the inbox and more likely to be engaged with.
How does STO work?
Send Time Optimization (STO) logs the engagement metrics of each subscriber in 1-hour slots throughout the day, resulting in 24 slots in total.
An optimality score is calculated for each time slot by assigning weights to opens and clicks: opens have a weight of 0.4, and clicks have a weight of 1. The time slot with the highest optimality score is recorded as the "optimal emailing hour" for that subscriber.
Take, for example, Jane Doe as a subscriber. Her engagement history is stored per hourly slot:
{
"1": {
"clicks": 1,
"opens": 2
},
"2": {
"clicks": 0,
"opens": 1
},
...
...
...
"24": {
"clicks": 3,
"opens": 2
}
}
The example slot 24 has a score of 3.8 (3 clicks × 1 + 2 opens × 0.4) and will be chosen as the optimal email time for Jane Doe. Her slots are updated whenever Jane opens or clicks an email, and her optimal time is recalculated.
When a campaign is launched with STO, each subscriber's email is scheduled for their own optimal hour (based on customer's time zone) within the next 24 hours. Time-optimized emails are delivered at the beginning of each hourly slot.
Data inputs
The optimality score is built from two engagement signals in the subscriber's email history:
- Opens: weight 0.4
- Clicks: weight 1.0
These are the only inputs used in the calculation. The day of the week is not counted; engagement is aggregated into the same 24-hour slots regardless of the day it occurred.
Architect's STO doesn't comply with the implementation; the system only counts clicks (action code 2).
Because Apple Mail generates automatic opens, it can distort the hourly distribution of open data.
Send Time Optimization (STO), as described on this page, applies to the email channel only. The optimality score is calculated from email opens and clicks, and the optimized send time applies to email campaigns.
You can also enable STO for emails in journeys. Refer to Architect Send Time Optimization for further information.
FAQ
Q: What happens if the subscribers do not have past events, such as opens or clicks?
A: The campaign will be sent right away.
Q: When are the time-optimized emails sent?
A: These emails are sent at the beginning of each time slot.
Q: Can STO be used in A/B campaigns?
A: This feature is not supported in A/B campaigns.
Q: Can STO be used in recurring campaigns?
A: Currently, this feature is not available for recurring campaigns.
Q: Does STO count days of the week while calculating the scores?
A: The day of the week is not counted in this calculation.
Q: What happens if two slots have the same score?
A: The previous optimal hour is not updated until a new one has a higher score.
Q: What happens when Jane opens/clicks an email after her emails are set for the STO campaign? Is her optimal time for this campaign updated?
A: It is not updated. The campaign will be sent regarding her optimal time while her STO campaign is set.
Q: Can STO be used when an automated warm-up is enabled?
A: STO is not supported during the warm-up period.