4

I want to reject emails to my postfix server based on more than one criteria, specifically I want to block emails from Russian email addresses (or that contain Cyrillic characters, but this I suspect is harder) that are addressed to two specific recipients (but not if addressed to others).

I feel this should be straightforward especially since the 'mail from' and 'rcpt to' addresses are both supplied right at the start of the smtp negotiation. But I can't find a way to do this with postfix, and am not sure if I need some add-on package (milter?).

4

Add in a restriction class. For example:

/etc/postfix/main.cf:
smtpd_recipient_restrictions =
    check_recipient_access hash:/etc/postfix/recipient_access

smtpd_restriction_classes = no_russians
no_russians = check_sender_access pcre:/etc/postfix/no_russians


/etc/postfix/recipient_access:
recipient1@mydomain.com     no_russians
recipient2@mydomain.com     no_russians

/etc/postfix/no_russians:
/\.ru$/ REJECT
  • Thank you, this is the best solution for my specific situation I think, except that the 'no russians =' line should not be indented. I have it working now! Instead of smtpd_recipient_restrictions it is also possible to use smtpd_relay_restrictions if this is more appropriate. – gogoud Sep 30 '15 at 10:43
2

Basically copy/pasting from http://code.metager.de/source/xref/postfix-debian/examples/smtpd-policy/greylist.pl#257 and adapting as we go, here is a simple Perl script to implement no_ru.pl as a simple check_policy_service script. See http://www.postfix.org/SMTPD_POLICY_README.html for how to hook it in.

Untested, YMMV, etc. You probably need to use and perhaps initialize a few facilities like syslog -- try this from the command line first.

# Unbuffer standard output.
#
select((select(STDOUT), $| = 1)[0]);

#
# Receive a bunch of attributes, evaluate the policy, send the result.
#
%attr = ();
$ru_sender = $ru_rcpt = 0;
while (<STDIN>) {
  if (/^\s*sender=.*\.ru\n/i) {
     $ru_sender = 1;
  } elsif (/^\s*recipient=.*\.ru$/i) {
     $ru_rcpt = 1;
  } elsif ($_ eq "\n") {
    if ($verbose) {
      syslog $syslog_priority, "ru_sender %i, ru_rcpt %i", $ru_sender, $ru_rcpt;
    }
    $action = ($ru_sender && $ru_rcpt) ? "reject" : "dunno";
    syslog $syslog_priority, "Action: %s", $action if $verbose;
    print STDOUT "action=$action\n\n";
    %attr = ();
  } else {
    chop;
    syslog $syslog_priority, "warning: ignoring garbage: %.100s", $_;
  }
}
  • Thanks for this worked-through suggestion. This type of approach might be really good in some more complex instances but the use of smtpd_restriction_classes as suggested by prabbide seems to me more elegant in this case. I may come back to your code in the future though! – gogoud Sep 30 '15 at 10:46
1

Have a look at the smtpd_recipient_restrictions and smtpd_sender_restrictions directives. Using those you can configure hash maps containing the filters you desire.

smtpd_sender_restrictions = check_sender_access hash:/etc/postfix/sender_access

/etc/postfix/sender_access:
.ru                       REJECT
someone@domain.com        REJECT

See also http://www.postfix.org/ADDRESS_VERIFICATION_README.html and http://www.postfix.org/SMTPD_ACCESS_README.html

  • but as I understand it this will 'OR' the restrictions not 'AND' them. That is, it will reject all emails from '.ru' regardless of recipient and all emails from someone@domain.com - I want to reject emails from '.ru' but only if addresses to two specific recipients. – gogoud Sep 22 '15 at 7:55
  • Sorry, misread your question. Have a look at Postfix Access Policy Delegation at postfix.org/SMTPD_POLICY_README.html. You can use it to extend basic filtering with more complex policies written in Perl. – Lambert Sep 22 '15 at 8:03
  • This is probably a way of doing it, but very complicated (not least because I would have to learn Perl...) - do you know of an easier way? – gogoud Sep 22 '15 at 11:20
  • You can use a number of other scripting languages. What would you prefer? The linked document from @Lambert's comment is fairly detailed; what you are asking should not be very hard. – tripleee Sep 28 '15 at 4:23

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