This shows the Inbox folder selected for an IMAP account named fm.em. Outlook Express is Working Online; in other words there is an active connection to the Internet, either dial-up or a permanent link.
A mail item - "Yom Terua - A DAY TO COME" - has been selected, but because OE has been configured not to automatically download messages in the preview pane the body of the message has not yet been downloaded. The size column indicates that this mail item is 113KB so if we were to Press Space to read it, we could reasonably expect the download to take a moment or two on a dial connection.
The small envelope icon next to each message indicates whether or not it has been downloaded. If the icon shows an open envelope then the message has been downloaded, which means it will still be available for reading and replying when you go offline. In this example, only one message - "Fastmail with Outlook Express" - has so far been downloaded and it includes one or more attachments, as indicated by the paperclip icon.
After making a dial-up IMAP connection you can selectively download the messages you want to work with offline and then disconnect. This is very efficient because you only download what you need and so minimise the time spent online. You can usually tell from the sender, subject, and message size whether or not you want to read it. Any item that you clearly don't want, such as junk mail, can be deleted immediately; no need to download since you have no desire to read it.