portmaster -dB mail/postfix
echo 'sendmail_enable="NO"' >> /etc/rc.conf
echo 'sendmail_submit_enable="NO"' >> /etc/rc.conf
echo 'sendmail_outbound_enable="NO"' >> /etc/rc.conf
echo 'sendmail_msp_queue_enable="NO"' >> /etc/rc.conf
echo 'postfix_enable="YES"' >> /etc/rc.conf.local
echo "NO_SENDMAIL=true" >> /etc/make.conf
service sendmail stop
/usr/local/bin/newaliases
service postfix start