The effect that these basic elements of email marketing may have on your metrics may surprise you.

Open rates are a tried-and-true email metric. As Matt Laudato, senior manager of big data and analytics for Constant Contact, puts it, “An email that’s never opened is an email that never has a chance for that click [and] never has a chance for that conversion.”

But are marketers doing everything in their power to optimize this metric?

New data from the small business email marketing services provider suggests that there are a number of fundamental factors that can significantly influence companies’ open rates. Based on the company’s analysis of more than 100 billion customer emails sent primarily by small businesses in 2014 and 2015, here are four basic elements of email marketing that marketers should take into account when evaluating their email campaign performance.

List size

Segmentation is hardly a novel concept. However, Constant Contact’s data reinforces the value of slicing and dicing one’s customer base to support personalization. According to the study, campaigns sent to 35 (yes, a super-targeted 35…) subscribers or fewer generated open rates of 55%, trumping the average of 22%. Campaigns sent to 7,500 subscribers or fewer produced an average open rate of 14%.

“Inside any large lists there are small, exclusive lists waiting to be discovered,” Laudato says.Indeed, Laudato says there are essentially two ways to segment a list: Start with a large list and narrow it down or just start with a small and exclusive subscriber base. Marketers who email to smaller audiences compared to those who “spray and pray,” he says, often generate higher interest and engagement because the messages are more relevant.

To better identify segments within a list, Laudato recommends following a three-step methodology: Test, measure, repeat. Just make sure to give it a try. After all, the only thing worse than not segmenting based on tested results, according to Laudato, is not segmenting at all.

Domain name

Think what follows a customer’s “@” symbol is irrelevant? Think again. According to the study, emails sent to Comcast, Verizon, Cox, and SBC Global domains experience the highest open rates, while messages sent to Gmail, AOL, Hotmail, and Yahoo domains experience the lowest.

Although Constant Contact doesn’t have any data as to why this might be the case, Laudato hypothesizes that it’s because the bottom four domains are among the oldest and, in turn, generate a lot of churn.

“The longer subscribers have been on a list, the less likely they are to engage,” he notes. “People get stale on lists, and they lose interest in what you’re talking about.”

Industry

Every industry faces its fair share of challenges—and for certain sectors, generating open rates can be one of them. Nonprofit organizations generate the highest open rates with a 29% average, according to the study, while B2C and B2B companies produce averages of 23 and 20%, respectively.

When looking at specific verticals within the nonprofit category, religious organizations achieve the highest open rates (38%), followed by medical services (32%) and associations (32%). Sports and recreation emails had the highest average open rate (26%) in the B2C space, followed by restaurants and bars (23%), publishing (23%), and entertainment (23%). As for B2B, professional services messages produced the highest average open rate (26%), with manufacturing and distribution (24%), marketing and PR (15%), and consultants (13%) trailing behind.

Compared to B2C and B2B organizations, nonprofits often do a better job of segmenting based on subscriber behavior, Laudato says. For example, an organization may separate those who made a donation last year from those who did not, he explains, and reach out to them first. This level of segmentation, he adds, is something marketers across all industries can benefit from.

“Behind every one of these email addresses—behind every click, behind every conversion—is a person,” he says. “It’s your responsibility as a marketer—even at the scale of having hundreds of thousands of people on your list—to do your best to identify what kind of person are they, who are they, and treat them as such.”

Mobility

Mobile has certainly shaken up the email marketing game. According to Constant Contact’s data, more than half (approximately 51%) of emails are opened via a smartphone or tablet—with a 38.8 and 11.9% breakdown, respectively.

So, it’s vital that marketers make their emails mobile responsive. In other words, “throw out the five-column newsletter,” Laudato says, “because it’s not going to work on the mobile device.”He also encourages marketers to keep their email text “short and sweet” and their images to a minimum so they render better on a mobile device. In fact, a previous study by the email service provider shows that messages with subject lines containing 50 characters or fewer, approximately five to seven words, have the most optimal open rates.

What now?

So, what exactly is the secret to generating higher open rates? According to Laudato, it’s having a short and compelling subject line, ensuring that the email is mobile friendly, and sending it to the right size list. However, he discourages marketers from trying to tackle all of this at once. Instead, he advises them to focus on optimizing one aspect at a time.

“Don’t bite off more than you can chew all at once,” he says. “Start with, ‘Can I come up with a shorter subject line?’ or ‘Are there two possible subject lines that I’m going to send out on Friday [where] one might do better than the other?’ Take the time to split your list in half and do a simple test. It’s as easy as making the effort to do a simple test and then monitoring what works and what doesn’t work.”