Today it is possible to set urgency hint using the "Custom command" option:
notify-send '%title' '%text' -i '%image'; wmctrl -r 'Thunderbird' -b add,demands_attention
However I'd like to use the GNotifier engine instead of the Custom one, especially because I'm using notify-send anyway.
What I'd like to see is a new option to optionally set the urgency hint in addition to showing the notification.
Thanks!