What’s the best time of day to send an email? How many links should you include? How long should the subject line be?

These were all questions examined in the “2013 Association Email Marketing Benchmark Report” by Informz, which analyzed more than 1 billion emails sent by more than 800 associations in an effort to provide associations with metrics to gauge their email marketing success.

One of the stand-out, yet unsurprising, findings this year is the importance of mobile. For the first time, mobile email readership surpassed desktop readership.

Adding credence to the mobile imperative, the study also noted that mobile readers tend to interact differently with email than those who read it from their desktops.

For example, mobile users click 20 percent less than desktop readers—most likely because emails that are not designed specifically for mobile are less reader friendly.

The study also found:

The more links the better. Similar to years past, the more links an email has, the higher the clickthrough rates (more than 70 links had the highest clickthrough percentage). The study also noted the importance of tone, language, and calls to action. For example, multiple calls to action in one email can confuse readers and cause them to not click on any links.

Focus your lists. The fewer number of recipients on your email list, the better the open rates. Content going to a select group of people is usually more targeted and in depth and thus carries greater value for readers. Emails that went out to 50 or fewer recipients had the highest open rates.

Keep your subject lines short. Emails with less than 10 words in the subject line had the best open rates.

“A good subject line will engage the reader by piquing their interest,” Sheri Jacobs, CAE, president and chief strategist of Avenue M Group, wrote in an ASAE Marketing Insights article. Jacobs recommended including a headline from within the email into the subject line.

Worry less about day-of-the-week delivery. Similar to last year, day of the week had little impact on open rates, but unlike previous years, Informz included an analysis of weekend delivery in 2012. The study found that while email delivered on a Saturday had the highest open rates, it also had the lowest clickthrough rates.

Another way to get more people to read your emails is to ask them what they want. When interviewed for Associations Now last year, Ron McGrath, chief technology officer at HighRoad Solution, recommended implementing a communication preference center where members can change or customize their email preferences.

“What better way to know what people want than to let them tell you,” McGrath said.

Whether you’re allowing your audience to tell you or you’re using a trial-and-error method to calculate what your audience wants, testing is what will ultimately determine the success of this type of marketing.

“One of the things that sets email marketing apart from other messaging mediums or marketing mediums is the ability to test and isolate systematically what works and what doesn’t work with your audience,” McGrath said. “At the end of the day, nothing is going to replace, or be better, than you testing against your own audience, because every audience is different.”

What metrics have you found useful for testing what your audience wants?

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