A Google approach to email.
Gmail is an experiment in a new kind of webmail, built on the idea that you should never have to delete mail and you should always be able to find the message you want. The key features are:

Search, don't sort.
Use Google search to find the exact message you want, no matter when it was sent or received.

Don't throw anything away.
1000 megabytes of free storage so you'll never need to delete another message.

Keep it all in context.
Each message is grouped with all its replies and displayed as a conversation.