ComScore's 2010 Digital Year in Review report may indicate that web-based email is declining, but marketers can't ignore the rising audience of mobile email users. A report from Merkle relayed by eMarketer indicates that email is still an important marketing channel.

Merkle, a customer relationship agency, found that nearly nine in 10 U.S. consumers (87 percent) checked their emails daily in 2010. Supporting Brafton's earlier reports about the rise of mobile email marketing, the study indicates that more than half of respondents (55 percent) had internet-enabled phones and they frequently checked email via mobile devices.

Nearly one-third of internet-enabled phone owners (31 percent) check their mobile email more than four times daily. Another 32 percent check their mobile email one to three times per day. This means more than half (63 percent) are daily mobile email users.

Additionally, Merkle's study disproves the theory that social media is replacing email as a marketing channel. Instead, the study found that social media users are more likely to frequently check their inboxes. Forty-two percent of social media users check their emails four or more times per day, whereas 26 percent of non-users check their emails at this rate.

With this in mind, marketers will want to prepare email marketing messages for mobile and social users that will catch clicks from subscribers. Just last week, Brafton reported that fresh content is key to engaging email recipients, with an Exact Target survey showing that nearly half of respondents (49 percent) unsubscribed to emails because of repetitive, boring content.