This plugin performs a number of checks on the HELO string.

HELO strings are very often forged or dubious in spam and so this can be a highly effective and false-positive free anti-spam measure.

helo.checks results can be accessed by subsequent plugins:

const h = connection.results.get('helo.checks');
if (h.pass && h.pass.length > 5) {
    // nice job, you passed 6+ tests
}
if (h.fail && h.fail.length > 3) {
    // yikes, you failed 4+ tests!
}
if (connection.results.has('helo.checks','pass', /^forward_dns/) {
    // the HELO hostname is valid
}

• helo.checks.regexps

  List of regular expressions to match against the HELO string. The regular expressions are automatically wrapped in ^ and $ so they always match the entire string.

• helo.checks.ini

cp node_modules/haraka-plugin-helo.checks/config/helo.checks.ini config/helo.checks.ini
$EDITOR config/helo.checks.ini

INI file which controls enabling of certain checks:

• dns_timeout=30

How many seconds to wait for DNS queries to timeout.

• valid_hostname=true

  Checks that the HELO has at least one '.' in it and the organizational name is possible (ie, a host within a Public Suffix).

• bare_ip=true

  Checks for HELO where the IP is not surrounded by square brackets. This is an RFC violation so should always be enabled.

• dynamic=true

  Checks to see if all or part the connecting IP address appears within the HELO argument to indicate that the client has a dynamic IP address.

• literal_mismatch=1|2|3

  Checks to see if the IP literal used matches the connecting IP address. If set to 1, the full IP must match. If set to 2, the /24 must match. If set to 3, the /24 may match, or the IP can be private (RFC 1918).

• match_re=true

  See above. This is merely an on/off toggle.

• big_company=true

  See below. This is merely an on/off toggle.

• forward_dns=true

  Perform a DNS lookup of the HELO hostname and validate that the IP of the remote is included in the IP(s) of the HELO hostname.

  This test requires that the valid_hostname check is also enabled.

• rdns_match=true

  Sees if the HELO hostname (or at least the domain) match the rDNS hostname(s).

• host_mismatch=true

  If HELO is called multiple times, checks if the hostname differs between EHLO invocations.

• proto_mismatch=true

  If EHLO was sent and the host later tries to then send HELO or vice-versa.

For all of the checks included above, a matching key in the reject section controls whether messages that fail the test are rejected.

Defaults shown:

[reject]
host_mismatch=false
literal_mismatch=false
proto_mismatch=false
rdns_match=false
dynamic=false
bare_ip=false
valid_hostname=false
forward_dns=false
big_company=false

• private_ip=true

  Bypasses checks for clients within RFC1918, Loopback or APIPA IP address ranges.

• relaying

  Bypass checks for clients who have relaying privileges (whitelisted IP, SMTP-AUTH, etc).

A list of =[,...] to match against. If the HELO matches what's on the left hand side, the reverse-DNS must match one of the entries on the right hand side or the mail is blocked.

Example:

yahoo.com=yahoo.com,yahoo.co.jp
aol.com=aol.com
gmail.com=google.com