A recent study by GetResponse showed that e-mail messages that included social sharing options generated 30% higher click-through rates than e-mails without a social option.
Messages with 3 or more sharing options generate 55% higher click-through rates.
These findings make sense if you consider that Twitter posts 55 million tweets a day and that the average Facebook user has 130 friends. This is Viral at its best, and if you give your audience an easy way to share your info, they will.
So next time when doing an e-mail campaign, make sure you include social sharing options.