You can run your own SMTP server and send through that. It's not hard to find a free one. However, a lot of hosts will reject email coming from a dynamically generated IP, so if the mail really has to get there, it's better to feed it through a remote hosting account with a domain name. The hoster may kill your account if you're caught spamming, however, so you better be dang sure the people receiving the emails want to receive them, and that you don't overload their mail server by bombing it with thousands of emails all at once.