qmail-smtpd     Receive message by SMTP from another host:                        |             MAIL FROM:<bill@irs.gov>     |             RCPT TO:<joe@heaven.af.mil>     |               |          Is $RELAYCLIENT set? No.     |          Is heaven.af.mil in rcpthosts? Yes.     |          Accept RCPT.       V                                qmail-queue     Store message safely on disk.                Trigger qmail-send.     |                  V                                qmail-send      Look at envelope recipient, joe@heaven.af.mil.     |          Is heaven.af.mil in locals? Yes.     |          Deliver locally to joe@heaven.af.mil.     V                             qmail-lspawn ./Mailbox                        |          Look at mailbox name, joe.     |          Is joe listed in qmail-users? No.     |          Is there a joe account? Yes.     |          Is joe's uid nonzero? Yes.     |          Is ~joe visible to the qmailp user? Yes.     |          Is ~joe owned by joe? Yes.     |          Give control of the message to joe.     |          Run qmail-local.     V                             qmail-local joe ~joe joe '' '' heaven.af.mil bill@irs.gov ./Mailbox                                   Does ~joe/.qmail exist? No.                Write message to ./Mailbox in mbox format.