Situation: You are big.isp. You have assigned a static IP address, say
1.2.3.4, to a dialup customer. The customer would like you to receive
mail for virt.dom and forward it to 1.2.3.4 whenever 1.2.3.4 makes an
SMTP connection to mail.big.isp.

These instructions assume that you have already installed serialmail and
ucspi-tcp, and that you are running qmail-smtpd from tcpserver -v as
described in /var/qmail/doc/FAQ 5.1, with tcpserver's messages piped
through splogger or cyclog.

These instructions _do not_ require that your customer install special
ETRN software. AutoTURN works with all SMTP clients.


1. Make a /var/qmail/autoturn directory:

      # mkdir /var/qmail/autoturn
      # chgrp qmail /var/qmail/autoturn
      # chmod 2755 /var/qmail/autoturn

2. Put the line

      +autoturn-:qmaild:7770:2108:/var/qmail/autoturn:-::

   into /var/qmail/users/assign, replacing 7770 with the qmaild uid and
   2108 with the nofiles gid. Run qmail-newu. Now mail for autoturn-blah
   will be controlled by /var/qmail/autoturn/.qmail-blah.

   Exception: If you have already been using qmail-pw2u to create
   /var/qmail/users/assign, put the above line into
   /var/qmail/users/append and then run qmail-pw2u as usual.

3. Replace

      /var/qmail/bin/qmail-smtpd
   
   with

      sh -c '
        /var/qmail/bin/qmail-smtpd
        cd /var/qmail/autoturn
        exec setlock -nx $TCPREMOTEIP/seriallock \
        maildirsmtp $TCPREMOTEIP autoturn-$TCPREMOTEIP- $TCPREMOTEIP AutoTURN
      '

   in the tcpserver invocation in your boot scripts. Reports from
   maildirsmtp will be sent to the same place as reports from tcpserver.

4. Make sure that there is an MX record for virt.dom:

      virt.dom IN MX 10 mail.big.isp

   Now any host on the Internet with mail for virt.dom will send it to
   mail.big.isp.

5. Put virt.dom into /var/qmail/control/rcpthosts. Now qmail-smtpd will
   accept mail for virt.dom.

6. Put virt.dom:autoturn-1.2.3.4 into /var/qmail/control/virtualdomains,
   and give qmail-send a SIGHUP. Now all messages for whatever@virt.dom
   will be delivered to autoturn-1.2.3.4-whatever.

7. Set up maildir delivery for autoturn-1.2.3.4-whatever:

      # cd /var/qmail/autoturn
      # maildirmake 1.2.3.4
      # chown -R qmaild 1.2.3.4
      # echo ./1.2.3.4/ > .qmail-1:2:3:4-default
      # chmod 644 .qmail-1:2:3:4-default

   Make sure to include the trailing slash on ./1.2.3.4/ and the colons
   in .qmail-1:2:3:4-default.


If you have more customers who want AutoTURN service, repeat steps 4
through 7 for them.

Security note: Both qmail-smtpd and maildirsmtp will run as qmaild;
neither one is protected against security holes in the other. You may
prefer to set up a separate autoturn user, and run maildirsmtp on a
separate TCP port under that user. One good choice is port 1789, the
Hello port. Here is the complete specification of the Hello protocol:

   The client connects to the Hello port on the server. It immediately
   disconnects. The server also immediately disconnects. The point of
   this protocol is to inform the server that the client is alive and
   reachable.

In this case your customer can use any program that can make a
connection to port 1789.