GMail is the internet based email system provided by Google.
Officially it is in beta and has been forever, but if you do get invited to us it you then get given invites to send to other people
Have a look at it's features....
here
It has probably the best feature that I am looking for in an email system and that is the ability to keep your message and conversations in threads. So if someone replies to an email, gmail will keep the messages in a thread similar to a newsgroup. As far as I know none of the other web based email providers do this (shoot me down if I'm wrong!). You also get over 2.5Gb of storage for free, which is pretty good.
I had a look at Yahoo mail the other day and I like it, lots of features, except that I didn't see how you could set the messages to be in threads. So I went straight back to Gmail.
Why don't you try it? if you don't like it...don't use it.