How to optimize email marketing

Hi guys, we're running a platform providing services to B2C clients. To activate/engage the customers, we send marketing emails to them. Our platform is fully custom coded. We use SES for sending.
Our goal: Generating max revenue while minimizing unsubscribe rates.
Currently we just send out more or less the same email to all DOI leads at the same time. I think that we should be able to (at least) reduce the unsubscribe rate by optimizing email frequency for specific kohorts.
How would you guys tackle this situation? How do we get from blasting the same email to all users at the same time to optimize content and frequency of the sendings?