The day might come where you would like to send mail as fast as you can, by still obeying rules from somebody else. This script sends mails as fast as possible to a mailserver and it will always open not more than 3 connections of 3 at the same time. I used this to register IDN-Domains at some point in my past. It is known to work with exim, but may also work with other MTA's.
Enjoy the IDN-Script.