What is Send gap (throttling)?
The minimum time between two emails from the same mailbox, randomised so sends don't fall on a fixed interval.
Thirty emails in thirty seconds looks like a script no matter how good the copy. A send gap of 15–30 minutes with random jitter spreads a mailbox's daily volume across the working day and makes the pattern look like a person at a keyboard. The gap and the daily limit fit together: 30 sends at 20-minute intervals is a ten-hour day.