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man : rblsmtpd(1)
rblsmtpd(1) 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 mes-
sages.
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 sec-
onds, 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.
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rblsmtpd(1) rblsmtpd(1)
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 legiti-
mate 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-envi-
ron(5)
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rblsmtpd(1) rblsmtpd(1)
http://cr.yp.to/ucspi-tcp.html
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