This is usefull when you have internet connection problem or any problem that make the mail server pending all outgoing mail. After there is ix to the problem, you need to force send all the pending mail
cd /var/qmail/bin
./qmail-qstat
./qmail-qread
./qmail-tcpok
ps axl|grep qmail-send
kill -s ALRM nnn
replace the nnn with value you see on ps axl command