man qmail-smtpd excerpt:
Unacceptable envelope sender addresses. qmail-smtpd will reject every recipient address for a message if the envelope sender address is listed in, or matches a POSIX regular expression pattern listed in, badmailfrom. A line in badmailfrom may be of the form @host, meaning every address at host. For more information, please have a look at README.qregex.