Seeking guidance from Experts

The company I work for has been around for 12 years and we just now begun our email marketing. We started by sending a blast to our clients from last year's first quarter and it went so-so. This was through Mailchimp. We got a some bounces and spam.

Since EMP's like Mailchimp could block you for too many spam complaints, we decided to create a Gmail account that lets you send emails. We tested with clients 2 years prior, and it went bad. So bad our gmail account got blocked because of too many spam. My question is, what's the best way to email our past clients that havent opted along with emails that may not work anymore. Keep in mind, they haven't opted to receive marketing emails. We are sending them a newsletter to subscribe to our email list before we send marketing emails. We tried this and got too many bounces for the year of 2014.

How can we strategize this? We don't want to keep creating different gmail accounts to send emails because of the spam complaints our list is getting. The more back we go, the more spams we are likely to get. Good news is that our boss only wants us to go 5 years back instead of 12 years.

How would you guys tackle a list of clients whom you've never sent an email campaign to without them opting in or you not knowing if their email works or not. In addition, the list includes the last five years of clients your company has had. One last thing, these clients of ours are clients that gave us their email while they were booking a car with us.