RapLeap, a research company, conducted an interesting study of email analysis. They looked at social network memberships of 120,000 AOL, Gmail, Hotmail, and Yahoo users to gauge where they spend time online.
RapLeaf found that AOL and Gmail users tend to favor Facebook, while Hotmail and Yahoo users tend to use Facebook and MySpace equally. Twitter is the third-most popular social network, followed by LinkedIn.
According to the study results, Gmail users are more connected and have more friends on a social network, other webmail users however maintain more social networking profiles. Even if this is true, is it true in APAC market? If it is true, an email campaign to gain Twitter followers would be more efficient if targeting Gmail users (you can do so via Google content network).
You can only test to find out; integrate social media with your email marketing campaigns and sample the same amount of users for each email provider (Gmail, Hotmail, Yahoo).