According to U.S. Census data, more than 30 million small businesses contribute roughly half of the country's nonfarm GDP. For many of these small enterprises, the new millennium has ushered in a new challenge regarding how to market themselves. Traditional local outlets have dwindled while digital has consumed the world, and SMBs have been forced to respond.

Coinciding with the rise of digital media has been the rise of the millennial consumer. As this generation aged and climbed the ranks of enabled spenders, it became impossible to ignore the marketing world's fascination with reaching them.

Social media and millennials — perhaps rightfully so — became inexorably linked together, and businesses were told you need one to reach the other.

There's no denying millennials are heavy purveyors of social media platforms, but in haste of catering to this group, have small businesses begun to miss opportunities to connect via the channel thought to belong to Generation X? Yes, of course, we're talking about email.

Recent studies have shown email remains a vital channel in the marketing mix — even for millennials. In fact, one of the most telling comes from Campaign Monitor, which found that millennials lead all other generations in making purchase decisions based on email.

"When it comes to taking action based on an email, millennials are far more likely to do so," the report stated, noting that 58 percent of millennials "always" or "most of the time" donated to a nonprofit in response to an email while just 18 percent of respondents over age 55 did.

On top of that, a study by Campaigner found millennials to be the most likely generation to engage with marketing emails. Twenty-two percent of millennials said they were "very likely" to open a marketing email, compared to only 15 percent from the entire survey group. Furthermore, more millennials listed email (51 percent) as a method they use to interact with brands than they listed social media (47 percent).

"As social media-savvy as millennials are, when it comes to brand engagement, email is still the best medium to reach this group," says Seamas Egan, associate director of revenue operations, Campaigner. "Yet nearly half of these consumers are also taking to social to follow brands. Marketers should meet them where they are while being trepidatious about investing too heavily in what may be flash-in-the-pan platforms."

Many millennials are starting to take a calculated approach to handling their promotional email by setting up separate email accounts strictly for their brand and marketing communications. Yes Lifecycle Marketing found 58 percent of millennials have done this, compared to the overall number of consumers at 36 percent.

"Perhaps because their inboxes have become flooded with marketing emails in recent years, consumers across generations are opting for brand-only email accounts; but this isn't a bad thing for marketers," said Michael Iaccarino, CEO and chairman of Infogroup, parent company of Yes Lifecycle Marketing. "Brands need cross-channel communication platforms so they can reach the ever evolving consumer when they want, where they want, and how they want."

As proof mounts that email is a significant vehicle to reach millennial consumers, another report illustrates how small businesses might be missing out on taking advantage. Ripl unveiled a recent study indicating that SMBs rank social media posts above email, digital advertising and even their own websites for gaining new customers and engaging existing clients.

Often, the small business marketing budget is limited; Ripl found the majority of them spend $100 or less per month on marketing software tools and online advertising. It's possible, and likely, this might be a key factor in SMBs' reluctance to take up email marketing campaigns.

"What typically holds a small business back from implementing an email marketing program is the investment it will take to implement it, the time it will take to set it up, and the knowledge and skills to keep it going," Rhonda Bavaro writes in a recent SMA Marketing post.

But she also points out advances in email automation have made it more affordable to initiate and maintain effective email marketing efforts.

With more than half of Americans checking their email accounts more than 10 times a day, it's evident social media hasn't been the death knell for email that many predicted. In fact, with evidence showing the coveted millennial audience is still a heavy user of email, any small business would be remiss to not consider it as part of a marketing mix.