It's critical to have a mobile-optimized or responsive design site because that's where your customers are, said David Sasson, president and CEO of overstockArt.com, a distributor of high-quality wall art, during the opening keynote of last month's Retail Marketing Virtual Conference & Expo.

In this audio snippet from the event, Sasson explains that while some may think mobile is the way of the future, the reality is that it's happening now. The penetration of smartphones and tablets grows daily, and retailers need to be making their websites optimized for them.

"If there are any retailers listening [who] don't have a mobile-optimized site or responsive design site, it's really critical because your customers are shopping and they're looking [at your site] in a variety of different ways," Sasson said.

overstockArt.com's mobile strategy includes "having a mobile site and a mobile app, [and] improving emails on [mobile phones] because a lot of emails are being consumed today via mobile devices," Sasson noted.

Email, in fact, is a key part of overstockArt.com's overall marketing strategy. "You have to think about [mobile] when designing your emails, which for us has been the best channel for marketing. Period. There hasn't been anything even close. It's not sexy anymore because everybody is doing it, but it's really very productive."

Push notifications are also huge for overstockArt.com, Sasson said, "especially when you're dealing with mobile and all of the spam filters and everything that's going on out there with emails. Email push notifications are to some degree replacing emails. We look at people visiting our site on their mobile phone as a touchpoint, not necessarily a place that we're looking for conversions. That's a huge thing for us to drive our communication."