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

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.

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

-tn   Change the timeout to n seconds.

       Blockedclients

       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.

       -rbase
              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.

       -abase
              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.

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

       Temporaryerrors

       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.

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.htmlrblsmtpd(1)

rblsmtpdoptsprog