DisableReverseLookups

From Qmail Info Wiki

Tcpserver is set by default (the -h option) to perform reverse lookups. This can cause a degradation in performance when tcpserver does not receive a timely and/or valid reply. If reverse lookups are disabled, the corresponding log will only contain IP addresses rather than host names. To disable reverse lookups, add the "-H" option to the run script following the tcpserver command. The line below provides an example taken from http://www.qmailrocks.org/faq/?category=qmail#59.

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