|Well, yes. This is fairly simple to do using PHP (for example). But it requires programming knowledge. A simple Google will find other ways to send mass emails.|
I'm sure I don't need to say this, but you need to check with your ISP as to any restrictions they may have. More importantly, be sure that you are fully up-to-date with the laws in your country regarding mass emailing; in most countries it is a requirement that the recipient has given their express permission to receive such emails.