E-mail is perhaps one of the most important channels in customer retention, and yet many marketers aren’t taking full advantage of its many possibilities. This is what Silverpop’s latest study, released last week, said.

The new report, titled “2007 Retail Email Marketing Study,” reviewed opt-in practices, message content, creative design and opt-out management of the e-mail campaigns for one-hundred fifty major retailers in North America and the UK. The study reviewed the registration procedures, marketing messages and opt-out practices of companies including Coldwater Creek, Hershey Direct, Marks & Spencer and American Girl.

“We’re still seeing a lot of marketers who are not taking full advantage of what is available when it comes to e-mail,” said Silverpop Managing Director Mike Weston. “Retailers are faced with the challenge of retaining customers and e-mail is an excellent channel to build customer relationships.”

The report found that one of the biggest challenges for e-mail marketers is list growth. It suggested that a valuable method for adding to a company’s database is to include a registration box or link on the home page. Despite this fact, UK retailers are nearly twice as likely as US companies to bury opt-in requests within their Websites.

The study showed that more retailers today are merely asking for an e-mail address. In Silverpop’s 2005 version of this same report, it found that nearly four in ten retailers asked for names, physical addresses, and e-mail addresses. Additionally, twenty-four percent of retailers in 2005 required even more detailed information, like telephone numbers, personal interests and demographic information.

However, while in 2005, only thirty-seven percent of retailers requested just an e-mail address, a full sixty-one percent limited their request to just the e-mail address this year!

With a growing number of e-mail clients blocking images, the popular postcard-style layout has fallen out of favor among e-mailers. In 2005, the postcard format was the format of choice for fort-four percent of the e-mails reviewed by Silverpop. This year, styles were a little more varied. While twenty-six percent of e-mails were postcard-style, thirty percent were designed like letters or newsletters and nineteen percent featured a single pane of text and art atop rows or columns below.

While retailers’ e-mail layouts have changed, the incentives to buy have largely remained the same. In both 2005 and 2007, three in ten retailers offer “percent off” sales while eleven percent offer free or discounted shipping.

E-mail marketers are also keeping CAN SPAM-compliant by making it easy to opt-out of e-mail programs. In 2007, almost six in ten companies sent recipients wishing to opt-out to pre-populated Web forms, while only thirty percent of retailers did this in 2005. However, retailers still use this opt-out time as an opportunity to reconnect. This year, thirty-two percent of e-mail opt-out links led to a preference center allowing registrants to make changes to their subscriptions, while in 2005, only twelve percent did this.