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.
List of regular expressions to match against the HELO string. The regular expressions are automatically wrapped in
$so they always match the entire string.
INI file which controls enabling of certain checks:
Checks that the HELO has at least one '.' in it.
Checks for HELO where the IP is not surrounded by square brackets. This is an RFC violation so should always be enabled.
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.
Checks to see if the IP literal used matches the connecting IP address.
Requires the HELO argument ends in a valid TLD if it is not an IP literal.
Bypasses check_no_dot, check_raw_ip, check_dynamic and require_valid_tld for clients within RFC1918, Loopback or APIPA IP address ranges.
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.