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ru.unix
- RU.UNIX ----------------------------------------------------------------------
From : Andrey Lugovoy 2:5020/400 17 May 2004 10:37:16
To : Mark Sergeev
Subject : Re: Sendmail обратная зона DNS
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Hello, Mark!
You wrote on Fri, 14 May 2004 09:42:05 +0000 (UTC):
MS> Кто-нибудь использует проверку sendmail'ом на существование обратной
MS> зоны
MS> DNS для приходящих писем?
MS> Поделитесь впечатлениями, стоит это делать? У меня чего-то большие
MS> подозрения что будет отсекаться много нормальных писем... Хотя с
MS> другой стороны спам должен тоже срезаться.
недавно поставил вот это. юзеры не жалуются. режется ОЧЕHЬ много СПАМа.
совместно с spamassasin+drweb ваще жить стало намного легче.
divert(-1)
dnl ## NOTE: This M4 file is suitable for sendmail
dnl ## 8.12.x . To use it with 8.10.x or 8.11.x, a one line
dnl ## change is required. Comments indicate which lines
dnl ## to change (to comment or uncomment)
dnl ################################################################
dnl ##
dnl ## This is a HACK to reject mail from connecting clients
dnl ## without proper rDNS (reverse DNS), functional
dnl ## gethostbyaddr() resolution.
dnl ##
dnl ## Use as:
dnl ##
dnl ## HACK(require_rdns)
dnl ##
dnl ## An optional second argument is available, and must be
dnl ## either `OK' or `REJECT'. With the second argument,
dnl ## the decision to reject depends on the recipient, and
dnl ## is based on access table entries for that recipient.
dnl ## The second argument gives the default assumed for
dnl ## recipients without access table entries. Currently,
dnl ## only the first letter of the second argument is
dnl ## checked.
dnl ##
dnl ## Note that the second argument makes no sense unless
dnl ## FEATURE(`delay_checks') is also in effect. It is
dnl ## best for the `delay_check' line to come first. This
dnl ## is not strictly required, but will avoid a warning
dnl ## message.
dnl ##
dnl ## The basis policy is to reject message with a 5xx
dnl ## error if the IP address fails to resolve. However,
dnl ## if this is a temporary failure, a 4xx temporary
dnl ## failure is returned. If the look succeeds, but
dnl ## returns an apparently forged value, this is treated
dnl ## as a temporary failure with a 4xx error code.
dnl ##
dnl ## EXCEPTIONS:
dnl ##
dnl ## Exceptions based on access entries are discussed
dnl ## below. Any IP address matched using $=R (the
dnl ## "relay-domains" file) is excepted from the rules.
dnl ## Since we have explicitely allowed relaying for this
dnl ## host, based on IP address, we ignore the rDNS
dnl ## failure.
dnl ##
dnl ## The philosophical assumption here is that most users
dnl ## do not control their rDNS. They should be able to
dnl ## send mail through their ISP, whether or not they have
dnl ## valid rDNS. The class $=R, roughly speaking,
dnl ## contains those IP addresses and address ranges for
dnl ## which we are the ISP, or are acting as if the ISP.
dnl ##
dnl ## If `delay_checks' is in effect (recommended), then
dnl ## any sender who has authenticated is also excepted
dnl ## from the restrictions. This happens because the
dnl ## rules produced by this HACK() will not be applied to
dnl ## authenticated senders (assuming `delay_checks').
dnl ##
dnl ## ACCESS MAP ENTRIES:
dnl ##
dnl ## Per-user entries:
dnl ##
dnl ## The per-user entries are of the form
dnl ## rdns:user OK
dnl ## where the RHS should be `OK' or `REJECT'. If `OK' is
dnl ## used, mail addressed to this user is not blocked on
dnl ## rDNS problems. If the value is `REJECT', it is
dnl ## checked. The second argument to the HACK() enables
dnl ## this feature, and provides the default for users with
dnl ## no entry.
dnl ##
dnl ## Note that the user in "rdns:user" is the user part in
dnl ## the mailer triple after address parsing. For a
dnl ## virtual address, this will be the user after
dnl ## virtusertable processing. If the mail is addressed
dnl ## to "user+detail" the "+detail" is stripped before
dnl ## this checking.
dnl ##
dnl ## If the recipient is on another host, then the key
dnl ## actually looked up is "rdns:@host." with the "host"
dnl ## being the destination to which we will send it. In
dnl ## some cases, this might come from a mailertable
dnl ## entry. It is not possible to individuate the
dnl ## decision for remote recipients. Note that the "."
dnl ## might be needed after the hostname. It is best to
dnl ## use the output of
dnl ## echo "/parse address" | sendmail -bt
dnl ## to decide what goes in the access map.
dnl ##
dnl ## IP address entries:
dnl ##
dnl ## Entries such as
dnl ## rdns:1.2.3 OK
dnl ## 1.2.3.4 OK
dnl ## 1.2 RELAY
dnl ## will whitelist IP address 1.2.3.4, so that the rDNS
dnl ## blocking does apply to that IP address
dnl ##
dnl ## Entries such as
dnl ## rdns:1.2.3 REJECT
dnl ## 1.2.3.4 REJECT
dnl ## will have the effect of forcing a temporary failure
dnl ## for that address to be treated as a permanent
dnl ## failure.
dnl ##
dnl ################################################################
divert(0)dnl
VERSIONID(`$Id: require_rdns.m4,v 1.7 2003/06/13 03:59:16 rickert Exp $')
divert(-1)
define(`_REQUIRE_RDNS_',
ifelse(defn(`_ARG_'), `', `',
lower(substr(_ARG_,0,1)), `o', `OK',
lower(substr(_ARG_,0,1)), `r', `REJECT',
`errprint(`*** Bad argument _ARG_ for require_rdns')'))
ifelse(_REQUIRE_RDNS_,`',`',
ifdef(`_DELAY_CHECKS_',`',
``errprint(`*** Warning: Optional argument to require_rdns needs
delay_checks
')''
))
PUSHDIVERT(9)dnl
SLocal_check_relay
ifelse(_REQUIRE_RDNS_,`',dnl
R$* $| $* $:$2 <?> <$&{client_resolve}>
,dnl
R$* $| $* $:$2 <?> <$&{client_resolve}> $&{rcpt_addr}
)dnl
R$*<?><OK>$* $@OK Resolves.
R$=R $* <?><$*>$* $@RELAY We relay for these
ifelse(_REQUIRE_RDNS_,`',`',dnl
R$*<?><$*>$+@$+ $:$1<?><$2>@$&{rcpt_host} use @host for remote
R$*<?><$*>$+ + $* $:$1<?><$2>$3 remove +detail
R$*<?><$*>$+ `$:$1<?><$2>$(access rdns:$3 $:' _REQUIRE_RDNS_ `$)' Check
rcpt
)dnl
ifelse(_REQUIRE_RDNS_, `REJECT',dnl
`R$*<?><$*>$={Accept} $@ $3 Bypass for this recipient
', _REQUIRE_RDNS_, `OK',dnl
`R$*<?><$*>REJECT $:$1<?><$2> mark rejections
R$*<?><$*>$+ $@OK bypass for others
',`')dnl
dnl ### The next line is sendmail version dependent
dnl ### Use this (with LookUpAddress)for sendmail-8.10 and 8.11
dnl`'R$+<?><$*>$* $:$1 $>LookUpAddress <$1> <?> <$2> <+ rdns>
dnl ### but use to following, instead, for 8.12
R$+<?><$*>$* $:$1 $>A <$1> <?> <+ rdns> <$2>
dnl ### end of version dependent text
R$*<$={Accept}><$+> $@ $2 OK or RELAY - whitelisted
R$*<REJECT><$*> $: $1<?><FAIL> REJECT - treat tempfail as fail
R$*<?><FAIL> $#error $@ 5.7.1 $: 550 Fix reverse DNS for $1, or use your
ISP server
R$*<?><TEMP> $#error $@ 4.1.8 $: 451 Client IP address $1 does not resolve
R$*<?><FORGED> $#error $@ 4.1.8 $: 451 Possibly forged hostname for $1
POPDIVERT
undefine(`_REQUIRE_RDNS_')dnl
With best regards, Andrey Lugovoy. E-mail: andrey.lugovoy@billing.ru
--- ifmail v.2.15dev5.3
* Origin: Demos online service (2:5020/400)
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