The increasing popularity of social networking sites and other forms of communication, including text messaging and cell phone use, are beginning to impact the effectiveness of email marketing, according to a new report from JupiterResearch.

In the report, titled "The Social and Portable Inbox: Optimizing E-mail Marketing in the New Era of Communication Tools," researchers found emerging forms of communication are reducing the use of email.

Twenty-two percent of email users said they use social networking sites instead of email, with more saying they have used instant messaging, text messaging, and cell phones instead.

"Consumers’ confidence in e-mail has become shaken by irrelevant communications and high message frequency, which are top drivers of subscribers’ churn and channel skepticism," explained David Daniels, Vice President, Research Director and Lead Analyst of the report for JupiterResearch.

"People receive such a high volume of e-mail that they are unable to pay attention to every message. It is so important for marketers to be relevant and succinct when they send messages to consumers’ inboxes."

In 2007, 51 percent of email users said email had led to at least one online purchase, and 47 percent said the same for off-line purchases. In 2008, the number of email users declined to 44 percent for online purchases and 41 percent for off-line purchases.

"Marketers need to be aware that consumers are using other forms of communication and must ensure their strategy adapts to consumers’ changing behavior," said David Schatsky, President of JupiterResearch.