45.6
LOCAL_RULESETS
SLocal_check_mail
R $* $: $&{client_addr}
R ${ourdomain} . $- $@ OK our domain
R $* $#error $@ 5.7.1 $: "550 cannot send out from the outside"
Here, the first rule transfers the value of ${client_addr} into the workspace. The $& prefix
(?§21.5.3 on page 793) prevents that macro from wrongly being expanded when the configuration
file is read. The second rule compares the domain part of your IP domain (that of
your internal network) to the workspace. If they match, the connection is from a host in
your internal domain space. If not, an error is generated in response to the MAIL From:
command.
Note that this rule set rejects all mail coming from outside your network, which might be
overkill (depending, of course, on what you want). It is really useful only at sites that have
two firewalls, one for incoming traffic and one for outgoing traffic. This rule set might go
on the outgoing firewall.
${client_addr} is transient. If it is defined in the configuration file or in the command line,
that definition can be ignored by sendmail. Note that ${client_addr} is not guaranteed to
be available in the check_compat rule set (?§7.1.5 on page 259). Note also that a $& prefix is
necessary when you reference this macro in rules (that is, use $&{client_addr}, not
${client_addr}).
21.9.19 ${client_connections}
Count of simultaneous client connections V8.
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