Ti posto i file interessati:

/etc/tcp.smtp

127.:allow,RELAYCLIENT=""
192.168.168.:allow,RELAYCLIENT=""
:allow
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/var/qmail/supervise/qmail-smtpd/run

#!/bin/sh
QMAILQUEUE="/var/qmail/bin/qmail-scanner-queue.pl" export QMAILQUEUE
QMAILDUID=`id -u vpopmail`
NOFILESGID=`id -g vpopmail`
MAXSMTPD=`cat /var/qmail/control/concurrencyincoming`
LOCAL=`head -1 /var/qmail/control/me`
if [ -z "$QMAILDUID" -o -z "$NOFILESGID" -o -z "$MAXSMTPD" -o -z "$LOCAL" ]; then
echo QMAILDUID, NOFILESGID, MAXSMTPD, or LOCAL is unset in
echo /var/qmail/supervise/qmail-smtpd/run
exit 1
fi
#if [ ! -f /var/qmail/control/rcpthosts ]; then
#echo "No /var/qmail/control/rcpthosts!"
#echo "Refusing to start SMTP listener because it'll create an open relay"
#exit 1
#fi
exec /usr/local/bin/softlimit -m 40000000 \
/usr/local/bin/tcpserver -v -R -l "$LOCAL" -x /etc/tcp.smtp.cdb -c "$MAXSMTPD" \
-u "$QMAILDUID" -g "$NOFILESGID" 0 smtp \
/var/qmail/bin/qmail-smtpd mail.miodominio.it \
/home/vpopmail/bin/vchkpw /usr/bin/true 2>&1
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Da notare che ho commentato l'if sull'esistenza di rcpthosts.Questo perchè ho dovuto cancellare quest'ultimo, in quanto, se presente, non mi fa spedire email a domini diversi dal mio.