To be successful, we have to humbly admit what we don't know and can't do alone.
Start from accepted values

Email productivity defined

These days our emails are so complex, and our email sending platforms put out a firehose of data. If we could only get one piece of data, what would it be? 

For most of us, it's whether the email we're sending is delivering our target audience to the web site. If 3% of the emails we sent resulted in a link-click. Then we're performing as well as can be expected. 

Email Optimization Shop: From the Boards: CTR or CTOR? 2020-Feb-1 by Jeanne Jennings

CTR gives you a good read on how interested your recipients are in your message. That’s pretty much all your recipients — everyone that you sent the email to minus those that bounced.

Let’s keep the math simple. If you send to 100,000 people, and 1,000 of them bounce, your CTR denominator is 99,000. If 4,000 unique people click on a link in your message, that’s a CTR of 4.0% (4,000/99.000). We know that 4.0% of the people we sent to clicked on our message. Let’s call this pretty good, since the latest Q2 2019 Epsilon Email Trends and Benchmarks Reports put average CTR at 2.9%.