Let's start with a familiar scenario: you have an old contact email database and you decided to use it as a way to do some prospecting. You use your business email address believing that your contacts will recognize your name and read your email. But then, you suddenly have trouble with your business email address: you start receiving DAEMON notices (email fail notification).
Congratulations: you are now spamblocked!
What happened to you could be the result of 2 possible scenarios: 1) lots of individual recipients complained to their respective ISP administrators about the newsletter emails (marked the mail as spam); or 2) emails never made it to the intended recipients because automatic ISP blockers (software) recognized the email as spam. One way that Scenario #2 will happen is if too many emails are sent to one domain at one time (e.g., 20+ emails sent to one domain will get you blocked).
It's important to note that large email domains (100 or more users) will have automatic blocking software - nothing can be done about that.
My advice - don't use this list again. Obviously, the list is bad in some way (How can I tell? You were blocked!). It is very likely that if you use the list again with ANY IP address, the emails will be blocked before they ever get to the email inbox (wasted effort).
Prospecting via email is difficult - but it can be done successfully. The best - and proven solution - is to build a prospect list by "renting" a high quality list based on your demographics to start. I have used USAData - but other companies are InfoUSA and V12 Group. These companies do 3 things as part of their service: they will rent an email list to you, transmit the email for you with their own IP addresses, and invite the recipient to opt-in to your own private list (which you can keep indefinitely).
What I described here is a standard operating procedure. "Yes," it is expensive and "No," there are never any guarantees. It's the cost of doing business.