sendmail Performance Tuning

4.1. What Happens During Email Reception

Just as we walked through an SMTP relay session in the previous chapter, let’s examine what happens when a message is received by an email server and stored in its message store. For the purposes of this example, let’s assume that we run sendmail version 8.9 as our MTA in background delivery mode on a typical operating system, we use /usr/libexec/mail.local as our LDA and Qualcomm’s qpopper as our POP daemon, and the message store uses the familiar 7th Edition mailbox format [SHO94] to store email. We’ll discuss the particulars of various mailbox formats later in this chapter, but for now note that 7th Edition mailbox format is just a fancy name for the default format in which email messages are stored ...