If you're going to send very large numbers of e-mails and want to limit how many of them are delivered per hour, you can "throttle" the Standalone E-mail Robot on a letter template or letter type basis. Within a letter template or a letter type, set the Maximum sent per hour by the Standalone E-mail Robot value. The Standalone E-mail Robot will limit itself to sending no more than this number of letters based on the given template or letter type each hour.
These settings do not apply when you manually send e-mails.