If messages you have sent to one or more recipients remain queued without being sent, this may be due to various reasons (for example, no connection to the recipient's mail server). In this case, your mail server will keep attempting delivery for a defined period of time. In the file “var/qmail/control/queuelifetime” you can see what that period is. By default, this is usually one week.
Qmail does not let you change this period of time for resending queued messages, but you can force Qmail to resend, or at least immediately retry sending, all queued messages. To do this, you will need to connect via SSH to your server.
Once connected, you need to send the signal “ALRM” to the process qmail-send so that Qmail will force queued messages to be resent:
kill -ALRM `ps ax | grep qmail-send | grep -v grep | awk ‘{print $1}’`