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rblsmtpd(1)


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)



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