NAME

       rblsmtpd  -  blocks mail from RBL-listed sites. It works with any SMTP server that can run
       under tcpserver(1)

SYNOPSIS

       rblsmtpd opts prog

DESCRIPTION

       opts is a series of getopt-style options.  prog consists of one or more arguments.

       Normally rblsmtpd runs prog.  prog is expected  to  carry  out  an  SMTP  conversation  to
       receive incoming mail messages.

       However,  rblsmtpd  does  not  invoke  prog  if it is told to block mail from this client.
       Instead it carries out its  own  limited  SMTP  conversation,  temporarily  rejecting  all
       attempts  to  send  a  message.  Meanwhile  it  prints one line on descriptor 2 to log its
       activity.

       rblsmtpd drops the limited SMTP conversation after 60 seconds, even if the client has  not
       quit by then.

OPTIONS

       -t n   Change the timeout to n seconds.

       Blocked clients

       If  the  $RBLSMTPD  environment  variable is set and is nonempty, rblsmtpd blocks mail. It
       uses $RBLSMTPD  as  an  error  message  for  the  client.  Normally  rblsmtpd  runs  under
       tcpserver(1); you can use tcprules(1) to set $RBLSMTPD for selected clients.

       If $RBLSMTPD is set and is empty, rblsmtpd does not block mail.

       If  $RBLSMTPD  is  not  set, rblsmtpd looks up $TCPREMOTEIP in the RBL, and blocks mail if
       $TCPREMOTEIP is listed.  tcpserver sets up $TCPREMOTEIP as the IP address  of  the  remote
       host.

       -r base
              Use  base  as  an  RBL  source.  An  IP address a.b.c.d is listed by that source if
              d.c.b.a.base has a TXT record.  rblsmtpd uses the contents of the TXT record as  an
              error message for the client.

       -a base
              Use base as an anti-RBL source. An IP address a.b.c.d is anti-listed by that source
              if d.c.b.a.base has an A record. In this case rblsmtpd does not block mail.

       You may supply any number of -r and -a options.  rblsmtpd tries each source in turn  until
       it  finds  one  that  lists  or  anti-lists  $TCPREMOTEIP.  It also tries an RBL source of
       rbl.maps.vix.com if you do not supply any -r  options.  See  http://maps.vix.com/rbl/  for
       more information about rbl.maps.vix.com.

       If you want to run your own RBL source or anti-RBL source for rblsmtpd, you can use rbldns
       from the DNScache (djbdns) package.

       Temporary errors

       Normally, if $RBLSMTPD is set, rblsmtpd  uses  a  451  error  code  in  its  limited  SMTP
       conversation.  This  tells  legitimate clients to try again later. It gives innocent relay
       operators a chance to see the problem, prohibit relaying, get off the  RBL,  and  get  the
       mail delivered.

       However,  if  $RBLSMTPD  begins  with a hyphen, rblsmtpd removes the hyphen and uses a 553
       error code. This tells legitimate clients to bounce the message immediately.

       There are several error-handling options for RBL lookups:

       -B     (Default.) Use a 451 error code for IP addresses listed in the RBL.

       -b     Use a 553 error code for IP addresses listed in the RBL.

       -C     (Default.) Handle RBL lookups in a ``fail-open''  mode.  If  an  RBL  lookup  fails
              temporarily,  assume  that  the  address is not listed; if an anti-RBL lookup fails
              temporarily, assume that the address is anti-listed. Unfortunately, a knowledgeable
              attacker can force an RBL lookup or an anti-RBL lookup to fail temporarily, so that
              his mail is not blocked.

       -c     Handle RBL lookups in a ``fail-closed'' mode. If an RBL lookup  fails  temporarily,
              assume  that  the  address is listed (but use a 451 error code even with -b). If an
              anti-RBL lookup fails temporarily, assume that the address is not anti-listed  (but
              use  a  451  error  code  even  if  a  subsequent  RBL  lookup  succeeds  with -b).
              Unfortunately, this sometimes delays legitimate mail.

SEE ALSO

       tcpserver(1),  tcprules(1),  tcprulescheck(1),   fixcrio(1),   recordio(1),   rblsmtpd(1),
       tcpclient(1),  who@(1),  date@(1),  finger@(1),  http@(1),  tcpcat(1),  mconnect(1),  tcp-
       environ(5)

       http://cr.yp.to/ucspi-tcp.html

                                                                                      rblsmtpd(1)