For years, there's been the expectation that email marketing would eventually go the way of the DVD, AOL, and other tech from the 1990s, especially as millennials and gen Z gravitate toward social, mobile, and other communication platforms. But more than 20 years after the first branded email message hit inboxes, email marketing remains stout as a business-to-business outreach and lead-generation tool.

"Email is the channel for serious communication, which puts it right in the sweet spot for B2B marketing," says Keith Sibson, SVP of product and marketing at PostUp, a provider of enterprise-level email, audience development, and monetization solutions. "No sensible person, millennial or otherwise, makes a serious product purchase decision for their business based on something they saw on Snapchat."

Mitchell Lapides, an email marketing veteran, agrees: "Lots of millennials don't use email for talking to each other, but when it comes to business, it's a persistent communication. If your list is of a high enough quality, you're sending out relevant content to that audience, and you can get them to respond to the appropriate calls to action, then the metrics are there to be monetized."