159606 sending mass email

I need to be able to send mass emails safely to thousands of emails address that I have for certain business niches. I don't want to send it from client's domain but use another one just in case. Most of the emails will be optin emails but then we'll have emails not on our lists. I need an email or email account from where I can send thousands of emails without any problem or limitation. And if possible track if users read the email or not. I'll be importing one list then send email, then another list and resend, and I would like to track the results. This should be pretty easy to use. I also need to avoid duplicated entries amongst all the lists, so that I don't send the same message to the same email. Can you help me with that?