Email send throttling finishing 1hr earlier

Question

Why is email send throttling in Marketing Cloud finishing earlier than expected? I did a User-Initiated send to 190k contacts throttled from 4:30pm-8:30pm with a max limit of 50k/hr. I would expect it to finish at 8:30 or close to it, however it finished 1hr earlier at 7:35pm. Our time zones are set up correctly.

Also does anyone know what the actual throttling behaviour is? Is it sending the max limit as a large batch send precisely on the hour or drip feeding every few minutes throughout the whole throttling window?

Answer 1

Send throttle doesn't spread the batch sends throughout the hour, it basically sends the 1st batch as soon as possible and waits for another hour to send 2nd batch and follows the rest.

In your scenario, you had the total of 190K with a max limit of 50K in Send throttle option which makes 4 batches and sends as 50K at 4:30pm, 50K at 5:30pm, 50K at 6:30pm and 40K at 7:30pm.

Also, below is the note from the documentation:

NOTE Setting a throttle for a job does not insure that a certain number of emails send during a particular time period. The throttle approximately insures that the system does not send a greater number of emails than the throttle limit during the specified time period. However, the system may send less due to system load, message complexity, or deliverability issues.

Reference: Send Throttle