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)
Free and Open Source Software