|You have had the answer. If your Email provider is not blacklisting you then it has to to the recipients and there is nothing you can do about that. If the Emails were bounced you would know about it.|
The only other alternative is that your email address has found its way onto an Email blacklist somewhere as a recognised spammer.
As Wanderer quite rightly points out, anyone sending out 1500 emails a week through a personal Email account is just asking for trouble. That is eight Emails an hour, every hour of every day for a week. Not what personal Email accounts were designed for. You should have been using the Email account of the company you were working for, they did have one, didn't they. So why use your personal account.
I once worked for a company, a small company with only a handful of employees. The job required me to send Emails on behalf of the company. In order to do this the company gave me my own company Email address, a simple and costless thing to do for someone with a business Email account. I would never have dreamt of using my personal Email account to do it. During the time I was with them I probably sent no more than 200 emails in total, most of them sitting at home in front of my own computer. When I left the company, the Email address was cancelled.
So you see, your claim to be sending 1500 emails a week on behalf of a company using your personal Email account just does not have the ring of truth about it.