Use the system's notifier

Is there a way to use the system’s notification functionality to send an email from a Bash script? If so, how?

I’d like to send a notification when a torrent is completed and transmission generates the event that triggers the file associated with the script_torrent_done_filename property.

# create_notification 
This program serves for creating messages which will be send to the user.
Usage:
         /usr/bin/create_notification -s [restart,error,upate,news] 'text of the message'

use examples:

MAILTO=""
# m h  dom mon dow  user  command
10 * * * *  root  create_notification -s news $(ifconfig pppoe-wan|grep "inet addr:"|awk '{print $2}'|awk -F : '{print $2}')