I am after the same type of code, I already have created a mailing list manager with 2500 subscribers but now find myself with a potential of at least 50,000 more subscribers with multiple lists .....
My current manager works using a cron job with a command of:
wget http://www.DOMAIN.com/script.php
and uses the header tag to refresh to avoid script timeouts ....
I cannot use a manager like listserv as I need to completely re-write so it looks in uniform with my other sites/software ..
Basically i need the method or advanced send algorithm that is used, not the pretty forms and list management functions, I have them already ...
Scott.