Email Communities: 1.3 Billion Accounts

It might be over-reaching to describe every population of application users as an actual community, but each might be considered a passive, or potential community.
And much as instant messaging platforms frequently are referred to as creating social networks, so email communities in some ways also create the foundation for social networks of extremely large size.

The leading email providers in the U.S. market, for example, can claim as much as 1.3 billion accounts.