I need to be able to host 1 to 3 million email accounts. I need the ability to inset banners and ofthe advertisments.

Does anyone know of a service that can handle that size of load?

you want to start an email service?
Probably you will need a dedicated server with good
smtp n pop features. The server should not choke.

you will need more than just 'a' dedicated server to host that kind of service. You might even need a specialized MTA / Web service developed that can scale well among multiple machines and possibly multiple locations.

Off the top of my head, Zimbra is a mail system that has Clustering and High Availability with Ad/Banner support. Check it out at http://www.zimbra.com/products/product_editions.html. These features are not in their open source edition however. So licensing a system that can scale to that many users will probably be $$$$.

Definitely, multiple servers.

Ugh.. You would require extremely fast server's which would be able to take high loads including POP3/SMTP/IMAP compatibility.. 'Hotmail' use Load Balancers in order to gain the full potential of the service they provide. You also tend to find that these services can be abused and lead onto Legal action been taken in order to resolve them. There are many hidden 'catches' it's not cheap either.

and i was thinking to open something like that on my PC at home... hmmm
ok i'll try to get a 200$ server and compete with $$$$$$ with many zero servers from hotmail and yahoo:)