Looking just at open and click rates gives you only a tiny piece of the email marketing picture, says Tim Watson, founder of email marketing consultancy Zettasphere. I couldn’t agree more.

To help marketers better understand which email metrics to focus on, Tim asked me and eight other email marketing experts to share our thoughts on the metrics that matter and how to use them to improve performance.

Here’s the advice that I shared:

When it comes to improving performance, the conversion rate is the most underused metric. Whether you’re looking at the performance of subject lines, email content, or landing pages, you should always be looking as far down the funnel as possible because all the elements of an email should be building toward that singular goal.

For instance, sometimes marketers think if they can just get subscribers to open their email—it doesn’t matter how—then they are more likely to convert because then they’re read the email copy. When looking at a single campaign that might be true, but if you tease, trick, or mislead subscribers into opening emails that aren’t relevant to them, then fairly quickly they will tune you out, regardless of how enticing your subject lines are. So a good subject line is actually one that preselects openers are most likely to convert.

Unfortunately, most brands are not able to use conversion rates strategically like this because they do not feed conversion data back into their email service providers. This forces them to rely on inferior—and even misleading—metrics like opens and clicks.

To see what the other experts said, check out the entire post on the Zettasphere blog.