When you’re sending a fundraising email to thousands (or hundreds of thousands) of supporters, every small component matters. Raising your average gift by just 50 cents will makes a pretty substantial difference when you’re talking about tens of thousands of gifts a year. So knowing whether a tactic works for you — general thematic messaging, express donate links, specific ask amounts, etc. — really matters!

But what’s the best way to evaluate a fundraising email’s effectiveness? From tracking opens and clicks and average gifts and unsubscribes — there’s a whole lot of valuable information to weed through to make those judgments.

If you only have one metric to look at: Gifts/opens — the percentage of donations received over the number of people who opened — will give you the best idea of the strength of your fundraising email. This metric helps rule out other factors that confuse success, like if you sent at a crappy time or your subject line left something to be desired, and boils everything down to one simple thing: How many people who read your email were motivated to donate?

Paying attention to your gifts/opens can give you a pretty clear sense of what is working in your messages, and what can be improved. You’re likely going to see best results from emails that convey urgency (Deadline: tonight!) or respond rapidly to breaking news (Did you see? Senator Horrible just voted to ban Skittles from the planet!), but your list will also have specific things they respond best to (Buttons?! Graphics with the candidates’s face?! ALL CAPS SUBJECT LINES!?!), and it’s your job to figure those out!

Measuring the success of your blast fundraising emails can be daunting, especially when each list is so unique when it comes to response rates and fundraising needs. Paying close attention to your gifts/opens rate, and working as hard as possible to maximize that percentage, is one of the most effective ways to optimize your fundraising emails.

Of course, I’d be foolish to advise you to ignore all other metrics — the strongest email program is evaluated by looking at all the numbers and how they fit together — but paying close attention to your gifts/opens rate is a good first step towards building the most effective email program possible.