POP and IMAP
Question : My Internet provider has its own e-mail program, but I use Outlook Express as my default
e-mail provider, both for the same account. Why do I receive some e-mail messages in Outlook Express but don't
get the same ones when I check mail with my ISP's e-mail software and vice versa?
Answer : E-mail programs these days usually use one of two standards: POP (Post Office Protocol) or
IMAP (Internet Message Protocol). Many Internet providers use POP mail, which is basically intended for use
with one e-mail program on one computer.
Most POP e-mail programs can be set to leave messages on the mail server for a certain amount of time after
you check your mail, or they can be set to delete the message from the server after you download it to your computer.
If your e-mail programs are both set to delete messages from the server after you retrieve them, you only get that particular
set of messages in the mail program on the computer you were using at the time.
If your Internet provider allows you to leave messages on the server for a short time even after you download them
the first time, try adjusting both mail program's settings to do so. That should let you get all the messages in both programs.
Service providers and mail programs that use the IMAP standard do not have to deal with this issue. Your messages
live on the server and you can keep your in-box up to date on different computers. However, you may have a limit as to how
many messages you can keep around on the mail server.