I am setting up a program so that I can e-mail all my clients by taking a list of clients in an excel spred sheet and e-mailing. Now, what is a really good e-mail program. A client is paying for this for my system so, I am not paying for this so cost is not a huge deal!

So break down, I need a good e-mailing program that I can send HTML documents. I want it to be a database that can be uploaded to. I want to have 50 identities who can send e-mails to thousands of people in a database?

What is a good Idea?