You can however be 100% sure that no-one gets your IP if you use a service like Hotmail or Yahoo (my preference, obviously) to email people. That's what I do! About 2 years ago, a "friend" of my daughter's figured out her hotmail pasword and used it to get into her e-mail account and send a nasty letter to all of my daughter''s friends in her address book (pretending she was my daughter). I was able to see the IP address from where she sent the e-mail and compare it to all of her other friend's IP addresses and figured out which friend had used her e-mail account. All you have to do (in hotmail) is to go to Options, Mail Display Settings, and click that you want Advanced Message Header Displays. Then you have all info of where any received e-mail came from....including the IP address of the sender.
I recommend that you send yourself an email using Hotmail and then take your own advice. Depending on your internet settings you may be in for a surprise: check for the "X-Originating-IP" header. In most cases your "100%" insurance isn't worth the 4 bytes of memory allocated for it.
(c)