1.) Exchange Server.

If your organization runs Microsoft Exchange Server, you can send mail within or outside of your organization’s network. Messages are usually stored on the e-mail server, but you can alternatively store them elsewhere (for example, on your computer). By default, Outlook creates a local copy of your mailbox on your computer and synchronizes with the server when you’re connected, so you can easily work offline if necessary.

2.) Post Office Protocol 3 (POP3).

When connected to a POP3 account, Outlook downloads (copies) messages from your e-mail server to your computer. You can choose to remove the messages from the server or to leave them there for a specified amount of time. If you access your e-mail account from multiple computers, you will probably want to leave messages on the server to ensure that they’re available to you.

3.) Internet Message Access Protocol (IMAP).

When connected to an IMAP account, Outlook stores copies of messages on your computer, but leaves the originals on the e-mail server. You read and manage messages locally, and Outlook synchronizes with the server when connected.

4.) Hypertext Transfer Protocol (HTTP).

Messages sent through an HTTP account (such as a Hotmail account), are in the form of Web pages that Outlook copies from your HTTP mail server and displays within the message window.

You can add multiple POP3, IMAP, and HTTP accounts (but only one Exchange Server account) to your Outlook profile.