I get a lot of email in my inbox. Because I have about 10 email accounts, things could get completely out of hand if I didn't set up a few rules. In email parlance, a "rule" or a "filter" is simply a way of sorting your email automatically as it arrives. Most email programs include rules. For example, in Outlook, you choose Tools|Rules and Alerts to access the Rules dialog box. Even Web-based email like GMail includes rules.
The principles are the same, no matter what email program you use. For example, I am notified whenever someone subscribes to one of our email newsletters. Rather than having to click and drag the email into the proper folder, I set up a rule to have my email program do it for me. When I receive an email that contains Logicaltips in the subject line, the email bypasses my inbox and is automatically filed in the Logical Tips folder.
I use GMail to monitor the discussion groups I participate in. Unlike most email clients, GMail doesn't use folders. However, it does use labels, so you can sort your email by applying labels then using a filter (aka rule) to keep your mail reasonably organized. To set up a label, click the Settings link at the top of the page and click the Labels link. Then type a name in the Create a new label box and click the Create button. Now click the Filters link. Click Create a New Filter. Because discussion group postings always come from the same email address, you can type it into the From box. Alternatively, you might filter emails by their subject line. Click Next Step. Now you tell what GMail should do with the email. You can bypass the inbox, apply a label, add a star, or Forward the email to another email address.
For my discussion groups, I click "Skip the inbox" and apply the label I have set up for the group. On the main GMail page in the Labels area, I can see how many emails there are, but they aren't cluttering up my inbox. Then I can read them when I get around to it.