As someone who provides a service, i.e. my technical know how, to whomever and whereever the customer may be, here in Phoenix, I am very mobile. As a consequence, I may be answering an email using my phone (Treo 700wx, which I love), using the Internet at a client site or sitting right here in front of the laptop in my office. I may be answering an email on a thread that is many days old. I may need the content of an email I sent 3 weeks ago, right now, right whereever.
IMAP, the internet message access protocol, makes my remoteness entirely possible. You see, in the good old days, web hosting companies only provided POP3 which required you to download the email to answer it. Get it? Download. As in, download to my PC, to my phone, etc.. After that, you better have that same download device around if you need to dig up that email thread. Same goes for emails you sent. IMAP uses the client-server model to manage your email. In other words, no download. It all stays on the server, every day and every where. Thank you, IMAP! In one small way, you make my small business better.