qmail

Chapter 6. Handling Locally Generated Mail

Mail comes from two conceptual places: inside your system and outside it. In this chapter, we look at mail that originates inside your system, mail generated locally on the host where qmail is running. We also take a first look at mail injected by MUAs on computers running on the same LAN, and mail injected by “roaming” local users elsewhere on the Net, which we address in detail in the next chapter.

qmail-queue

The only way to pass a message into qmail is qmail-queue. All of the other relay and injection programs, for both local and remote originated mail, call qmail-queue to queue a message and schedule it for delivery. This design has two advantages: it’s easy to write new frontends to inject mail because they only need to call qmail-queue to pass along the mail, and by replacing qmail-queue with another program that offers the same interface, you can create interestingly different systems, such as mini-qmail. (See Chapter 16 for details.) It also offers security advantages, because qmail-queue is one of the few set-uid programs (to qmailq, not root) in the qmail package, so it can write files in the queue directories.

qmail-queue is intended to be run from other programs, not from the command line, so it has an interface that only another program could love. It takes no command-line arguments and reads its input from two file descriptors. The first input is read from file descriptor and is the text of the message. qmail-queue ...