"A rule is a little piece of programming that tells Outlook how to handle certain email messages you get or send."

A rule is a little piece of programming that tells Outlook how to handle certain email messages you get or send. In some other mail clients, the term "filter" is used to mean the same thing.

To understand rules, you need to understand the basics of how your email flows into your Outlook client. Don't worry, this is pretty simple stuff.

When I send you a message, my computer doesn't talk directly to your computer. Instead, I create the message on my computer. When I hit send, that message is uploaded to my email server, which stores and then forwards the message to your email server. Then, when you download your messages, your email client brings the message down from your email server to your email client.

To be fair (and we'll talk about this in a bit), not all Outlook users download their email to their computer. Some read their email via Outlook Web Access, some use IMAP (Internet Message Access Protocol), and some keep their messages in Microsoft Exchange stores. In these cases, the message never transfers down to your computer -- and this affects how your rules will work. We'll get to that later.

Let's first look at the process where you get your messages. The rules engine kicks in when it's time for Outlook to download your messages, whether through a Send/Receive or when Outlook does it's regularly scheduled download. You can also use rules on outgoing messages, but that's much less common. In effect, each message you download has to pass through Outlook's rules engine before it goes into your inbox (somewhat like when you have to pass through a toll booth to get onto the Turnpike).

If you think about those toll booths, at least here in New Jersey, different vehicle types get charged different amounts. The toll booth attendant evaluates each vehicle, and based on whether it's a passenger car or an eighteen-wheeler, charges accordingly. I know toll booths have EasyPass and exact change lanes, but let's just use the attendant for this example.

Understanding conditions
Likewise, in Outlook, as the message passes through the rules engine, Outlook checks to see if the message meets any of the criteria set up by the rules. The rules engine is, in effect, the booth attendant, making an evaluation for each message flowing through, and then, depending on that evaluation, taking a specific action or actions.