man qmail-smtpd excerpt:
Unacceptable HELO/EHLO host names. qmail-smtpd will reject every recipient address for a message if the host name is listed in, or matches a POSIX regular expression pattern listed in, badhelo. If the NOBADHELO environment variable is set, then the contents of badhelo will be ignored. For more information, please have a look at README.qregex.