qmail-popup - read a POP username and password

          qmail-popup hostname subprogram

          qmail-popup reads a POP username and password from the
          network.  It then runs subprogram.

          qmail-popup is most commonly invoked from inetd as

             qmail-popup CHANGEME checkpassword qmail-pop3d Maildir

          with CHANGEME replaced by the fully qualified domain name of
          the local host.

          qmail-popup expects descriptor 0 to read from the network
          and descriptor 1 to write to the network.  It reads a
          username and password from descriptor 0 in POP's USER-PASS
          style or APOP style.  It invokes subprogram, with the same
          descriptors 0 and 1; descriptor 2 writing to the network;
          and descriptor 3 reading the username, a 0 byte, the
          password, another 0 byte, an APOP timestamp derived from
          hostname, and a final 0 byte.  qmail-popup then waits for
          subprogram to finish.  It prints an error message if
          subprogram crashes or exits nonzero.

          qmail-popup should be used only within a secure network.
          Otherwise an eavesdropper can steal passwords.  Even if you
          use APOP, an active attacker can still take over the
          connection and wreak havoc.

          qmail-popup has a 20-minute idle timeout.

          qmail-popup is based on a program contributed by Russ

          maildir(5), qmail-local(8), qmail-pop3d(8)

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