Email deliverability - fix emails going to spam

My email open rates used to be 16%. Over the past two weeks they've gone down to 8%. I think this could be because I upped the frequency of emails recently. A lot of the emails are going to spam all of a sudden. Interestingly, the click through rate hasn't been as affected as the open rate. I would like you to diagnose the problem, and work with me to improve deliverability, stop the emails going to spam, and improve rates and click through rates. Please only apply if you can prove you have fixed deliverability problems in the past, and helped other businesses prevent emails going to spam, and improved open rates. I'd like to see examples of your work with other clients. Look forward to working with you! Ollie