The online survey revealed that 44% of email users made at least one online purchase, and 41% made at least one off-line purchase, during the prior 12 months as a result of promotional emails. That might sound good on the surface, but those numbers are considerably lower than 2007, when the respective percentages were 51% and 47%.

Also, after years of seeing stable volumes of consumer-reported email for their primary, personal email accounts, this year's survey revealed a decline. Email users now report receiving a daily average of 24 email messages of all types (including friends/family, opt-in, work/school, spam and other) in these primary accounts--down from 41 per day in 2006.

JupiterResearch attributes the drop in overall email volume partially to a decrease in spam messages. But analysts say the declines also point to shifting communication channel usage patterns, particularly among young consumers.

Between 2006 and 2007, the numbers of email users ages 18 to 24 who reported receiving an average of 31 or more emails per day dropped from 21% to 13%, while the numbers who reported receiving this many emails among the total universe declined by just 1%, to 36%. And this year, the average daily number of emails reported by 18- to-24-year-olds was just 12.

Email users ages 45 to 54 also report declining numbers of emails--just 25% now report receiving 31 or more each day, compared to 42% in 2007. (However, this age group still receives the greatest volume--an average of 28 per day.) Among those age 55 or older, the number who report receiving 31 or more emails per day has declined from 42% in 2006 to 24% now.

"Marketers need to be aware that consumers are using other forms of communication and must ensure their strategies adapt to consumers' changing behavior," said JupiterResearch president David Schatsky.

Consumers reported that emails from friends/family grew to 34% of total emails (versus 32% in 2007). However, they reported stable or slightly lower percentages of other types of email messages, including opt-in messages--which now account for 25% of overall volume, compared to 26% last year.

Yet, JupiterResearch's surveys of email service providers confirmed an increase in the numbers of permission-based emails sent out. The researchers attribute the apparent disconnect between vendor numbers and those reported by consumers to two main factors: growing use of secondary email accounts, and marketers continuing to send emails to dormant accounts.

Lack of relevance continues to be the top reason for unsubscribing, with 50% of total email users reporting that they unsubscribe when the offers/types of content do not interest them. Of particular note to marketers, the percentage who unsubscribe to irrelevant messages is even higher among those who have made four or more online purchases during the past 12 months: 60%.

Frequency is the second-highest driver of unsubscribes: 37% percent of all users say they unsubscribe when they receive emails from a sender "too often." Not surprising, then, that 33% report that they unsubscribe from offers because they get "too much" email.

Moreover, 39% say they believe that signing up for permission-based email leads to getting more spam email, 30% say they don't trust that the unsubscribe link in email offers works, and 26% say they use the spam button to unsubscribe.

These behaviors and attitudes "are driven by the unfettered volume of spray-and-pray untargeted email offers, blurring the distinction between spam and permission-based email," the analysts conclude in the report, "The Social and Portable Inbox: Optimizing E-mail Marketing in the New Era of Communication Tools."

"Consumers' confidence in email has become shaken by irrelevant communications and high message frequency, which are top drivers of subscribers' churn and channel skepticism," said David Daniels, VP, research director for JupiterResearch and lead analyst of the report, stressing that it's clearly more important than ever for marketers to send relevant, succinct email messages.

The online survey, conducted in April, was designed and fielded by JupiterResearch and sent to a randomly selected sample from NPD's U.S. online consumer panel. A total of 2,460 consumers responded to the survey, which asked approximately 30 closed-ended questions about their behaviors, attitudes and preferences in regard to promotional email, mobile marketing, Web site search, and communications devices.

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