= spam/対策/bad_helo =

spamはHELO/EHLOが不正であることが多い。
  だが、受け取りたいメイルにも、...

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Blocking email on bad HELO/EHLO information
  http://faculty.cs.niu.edu/~rickert/cf/bad-ehlo.html

Possible blocking rules

The rules I offer (but do not recommend) attempt to avoid blocking our own users. These rules are offered as hints, with the expectation that you may need to change them to suit your needs.
Note that I have not tested using the rules directly as a HACK. I have tested them manually incorporated into my ".mc" file, where they are integrated into other local rules.

If a client has authenticated, then no check is done on the HELO name. If the client IP begins with a part in class $=R, then we assume that this is one of our own users. Again, no check is done.

If these tests fail, the email is rejected under any one of the following circumstances.

    The HELO name is one of our own IP addresses.
    The HELO name is one of our own hostnames.
    The HELO name is not properly qualified (contains no ".").

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https://www.howtoforge.com/community/threads/mail-server-flagged-as-spam-for-bad-helo-ehlo.79657/

Xhttps://mail-toaster.org/wiki/Badhelo

https://www.linuxmagic.com/best_practices/valid_helo_domain.html

{{{
The following bad example(s) will get rejected:

    HELO
    HELO localhost
    HELO localhost.localdomain
    HELO hostnameonly
    HELO 192.168.1.1 (just an IP)
    HELO [192.168.1.1]
    HELO .com (starts with a period)
    HELO fake..com
    HELO @(&$ (characters not normally allowed in domain names)
}}}


https://www.fehcom.de/qmail/fightspam.html

https://meta.discourse.org/t/550-bad-helo-host-impersonating-hostname/195811