--- /dev/null
+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.