Online shoppers received more e-mail marketing messages from retailers in 2011 than they did in 2010, according to data released by Responsys Inc. The e-mail marketing services provider says retailers, on average, sent each of their subscribers 177 promotional e-mails last year, up 16% from 2010.

Responsys based its findings on its tracking of e-mail marketing messages from more than 100 U.S. e-retailers. The company expects similar e-mail growth in 2012, says Responsys research director Chad White.

“During 2011, major retailers relied more than ever on cost-efficient e-mail marketing to reach their customers and generate sales,” he says. “But the growing challenge for marketers going forward is to gradually rely less on volume increases and more on increases in message relevance to drive success. Deploying better analytics, more triggered e-mails, and more segmented and personalized messaging should be key areas of focus in 2012.”

Last year’s growth in e-mail marketing was helped by a late season surge in those messages during the 2011 holiday shopping season. Responsys says that during November and December, the retailers it studied sent, on average, at least 41 promotional e-mails, a 20% increase from the 2010 holiday shopping season.