Sending speed options are as follows:
Default - is the normal sending speed of your account based on your package size which allows you to reach your quota per month.
1 connections at a time - About 15 an hour
1 connections at a time - About 30 an hour
1 connections at a time - About 60 an hour
2 connections at a time - About 120 an hour
3 connections at a time - About 500 per hour
3 connections at a time - About 1500 per hour
10 connections at a time About 3,000 per hour
25 connections at a time About 5,000 an hour
100 connections at a time About 10,000 an hour
200 connections at a time About 20,000 an hour
300 connections at a time About 40,000 an hour (Not recommend for email delivery)
400 connections at a time. About 50,000 an hour (Not recommend for email delivery)