Many of us have been inundated recently with spam appearing to be from ourselves, and even with Spam Assassin some inevitably slips through. Read more to learn how to use filters to sift your email.
Filtering allows your mail program to route mail to different folders based on the subject, sender, or other information in the message. Some common uses of filters are:
to take messages that Spam Assassin had added ">>>SPAM<<<" to the subject, and put them in a Junk folder;
to route mail from a mailing list (based on sender or subject) to a folder for just those messages;
to put personal mail (based on sender) into a folder of its own.
With the recent spate of spam you may want to route all messages from yourself into a folder just for that purpose. If you don't ever cc yourself on messages, you may prefer to route them directly to your junk folder or trash. Whatever you decide to do, there are a few of caveats when using filters.
If you just route the mail to a folder and leave it sitting there, you can quickly eat up your disk space (and your quota space if you're using webmail or are using an IMAP-configured mail client). You must regularly look through the folder and delete what isn't necessary to keep. If you are on webmail, you should offload things you are keeping long term to your own computer.
A filter is only as good as its rules, and occasionally human oversight is needed. Look through your folders to make sure there's nothing critical there that you haven't seen.
Filters work behind the scenes, and if you forget they're there it can be confusing. For instance, if you set up a filter to move all messages from yourself to a folder, and then a few months from now you cc yourself on a message, you may forget that you won't see that message in your inbox and assume that something is wrong. Review your filters occasionally to make sure you still need them.