Brafton has reported that marketers should offer email subscribers custom content, but now it seems mobile-ready content should also be a top priority. A new report from comScore reveals that mobile email is now mainstream.

According to the report, email usage via mobile devices has seen significant gains in the past year. In November 2009, roughly 50 million Americans checked their email on-the-go over the course of a month. Monthly mobile email usage shows 36 percent growth, with more than 70 million consumers checking their mobile inboxes.

Moreover, the report shows that more than 43 million Americans use their mobile email almost every day. This demonstrates 40 percent growth over last year.

Although comScore found that web-based email usage showed some declines last year, it remains one of the top web activities overall, reaching more than 70 percent of U.S. consumers on a monthly basis. Plus, the rise of mobile email bring new life to this channel.

Marketers planning their email content may have the best success targeting younger, male mobile users. Checking mobile emails was more common among men than women, and mobile subscribers between the ages of 12 and 44 represented the majority of on-the-go email users.

Brafton has reported that mobile users are inclined to search for timely information. With this in mind, brands may find they get a competitive edge by offering news headlines and trending content in their email newsletters.