Disable reverse DNS lookups on SMTP connections

To disbale the reverse DNS lookups on SMTP connections in qmail, you need to edit qmail-smtpd supervise script.

That file is located at /var/qmail/supervise/qmail-smtpd/run.
Look for for following line:

/usr/local/bin/tcpserver -v -R -l "$LOCAL" -x /etc/tcp.smtp.cdb -c "$MAXSMTPD" \

...& replace with this..

/usr/local/bin/tcpserver -v -R -H -l "$LOCAL" -x /etc/tcp.smtp.cdb -c "$MAXSMTPD" \