What, the astute reader asks, does this have with Procmail to do?
Well, Procmail is frequently used to handle mail. And Procmail can only look at what’s in a message’s headers. And since the headers might just contain more or less anything, trying to let Procmail figure out whom a message for is pretty futile. Nevertheless, this is something a lot of people are trying to do. If you are content with the answer “Procmail is the wrong tool for this,” you can stop reading now and skip to the next question. Let’s take an example. The following message looks like it was sent from foo@bar.net to nospam-list@nospam.org. And yet, it was actually sent by some mailing list package at nospam.org and landed in your inbox, because you’re a subscriber to nospam-list@nospam.
