Send time optimization and email throttling are separate features that can be used in email campaigns.
Send time optimization calculates the best time for each user to receive messages based on their individual behavior and engagement patterns, considering past open and click events.
On the other hand, email throttling controls the total email volume sent from your account. It evenly distributes the combined volume of all simultaneously launched campaigns according to the hourly limits you set, ensuring system stability and avoiding ISP rejections.
While send time optimization focuses on determining the best time to send messages to individual users, email throttling manages the overall distribution rate of emails across campaigns.