You can host a server yourself or use a version hosted by the company. If you are not concerned with privacy issues, it works like a traditional mail client.
He said he wanted a mail client, not a mail client that requires a self hosted server infrastructure or giving the email out.
> it works like a traditional mail client.
Except it's not just a client.
Wait, last time I checked, the API/Server wasn't free software? Did I miss something, or has the licensing model changed?