More than men, women are enthusiastic online communicators, and they use email in a more robust way. Women are more likely than men to use email to write to friends and family about a variety of topics: sharing news and worries, planning events, forwarding jokes and funny stories. Women are more likely to feel satisfied with the role email plays in their lives, especially when it comes to nurturing their relationships. And women include a wider range of topics and activities in their personal emails. Men use email more than women to communicate with various kinds of organizations. –How Women and Men Use the Internet (Pew Internet & American Life Project)
From the press release announcing the full study (available as a PDF).