The world apparently has a demand for an email service that is free, easy to use, secure, or whatever other attribute that makes hundreds of millions of people

The world apparently has a demand for an email service that is free, easy to use, secure, or whatever other attribute that makes hundreds of millions of people choose to use Gmail compared to any other client (SquirrelMail) or service (Yahoo). I'm sure Google's market influence had something to do with Gmail's success though.