Is email still the anchor for customer engagement, given the rise of mobile, social media, texting, websites and big data? With people joking that they don’t even know what email is, you have to wonder.

ExactTarget, which specializes in email marketing and other personalized marketing programs, argues that email is more central than ever before. And apparently, so would SalesForce.com, which agreed in early June to pay $2.5 Billion for the company.

Last week, at San Diego Interactive Day, ExactTarget’s Joel Book laid out the case for email, which he calls “the backbone of customer engagement.”

Email is still more widely used than any other channel, he argues. And the rapid spread of smart phones have greatly accelerated email’s capability. “Mobile is the new direct response,” he says. It is “all about marketing to the individual.”

Email also enables marketers to own their own audience. It’s a long way from 1976, when marketers used to “rent” an audience by buying SRDS books.

The challenge for marketers is to make sure that their email programs are well integrated into all their other programs, including social media, websites and mobile. Shoppers “want a seamless shopping experience,” says Book.

The best way for brands to respond to this need is to use direct response methods such as email to build “small, highly engaged communities.” Brands such as Scott’s Lawn Care have made a science of doing exactly that, tying personalized emails to entire programs for garden care.