How does the email limit of 300 per hour work? Is it
1. Per each clock hour (e.g., 3:00 to 4:00, 4:00 to 5:00),
2. The number of emails in a sliding window of the previous hour from
now (e.g., if it is now 3:25, then 2:25 to 3:25),
3. When you hit the limit, you can't send for the next 60...