More and more users are taking their email on the road with connected devices (i.e. Blackberry, Palm, Windows Mobile phones), so staying connected is easier than ever. It can get a little complicated, though, if your mail account isn't set up properly for your growing needs. If you're struggling because some of your email is *only* available at your desk, and some of it is *only* available only on your phone, read on for (hopefully) some help...
Most consumer (and business) email accounts are set up as POP (or POP3) accounts. POP stands for Post Office Protocol...and this kind of email account works a lot like the real Post Office. The server (the Post Office) holds your mail/email until you 'pick it up' by clicking 'Send/Receive' in Outlook Express, or some other email client. From that point on, the mail only exists on your local computer...the copy on the server is deleted afte the mail is downloaded to your local computer. Since mail can only be delivered to one place by the post office, you also can't get access to those messages from any other computer.
The other major option for email is called an IMAP account. With IMAP, the mail always stays on the server. When you want to view it, you open up a program (like Outlook) and that program goes out the server to get a list of messages for you to view. You read, compose, reply, forward, and delete the messages just like in a POP account, but you're just looking at a local copy of what the server is holding for you...the messages don't actually exist on your computer. This allows you to move to a different computer, access your email account, and see the exact same message list. IMAP gives you 'anywhere-access' to your messages.
The downside of IMAP is that it requires you to be connected to the Internet constantly...it's not very good at working offline. If you have a steady, high-speed Internet connection, this isn't usually a problem...but it's worth considering if you use dial-up.
Cost-wise, there isn't much difference...but IMAP is slightly more expensive. This is especially true if you have *a lot* of email, and you're not the deleting kind of user, because you have to pay for constant online storage of those messages.
Here are links to other discussions about IMAP vs. POP mail accounts.
http://www.helpdesk.ilstu.edu/kb/index.phtml?kbid=1172
http://www.washington.edu/computing/windows/issue13/imap_pop.html
http://www.imap.org/papers/imap.vs.pop.brief.html