Sending speed by default is 1 per minute. You can speed up sending if you shorten the schedule window (i.e. from 8AM to 10AM vs 8AM to 7PM). Basically take all your sending email addresses, sum them up for the total daily volume, then we divide that by the sending window and try to send all the emails within that window up to 10 per minute. 10 per minute is a lot, and sending a lot of emails like this is a great way to burn your domain or damage your deliverability so be careful!.