Koha user can send messages in queue due to various reasons. Certain messages in Koha set to send in midnight. Often libraries running Koha on desktop machine shut down PC after working hours. In this situation, messages can't send. If you are also hurry to send messages generated at once, apply following commands:
1. Load environmental variables
sudo su
export PERL5LIB="/usr/share/koha/lib"
export KOHA_CONF="/etc/koha/sites/library/koha-conf.xml"
2. Push messages in queue
cd /usr/share/koha/bin/cronjobs
./process_message_queue.pl