Unfortunately you can't customise the email body.
You can change the subject though - look in <IMC>\server\conf\qvdm.conf
Near the bottom there is a configuration option for changing the email subject. You'll need to restart jserver after making changes.
You can use a few different variables, and change the order a bit to make it more meaningful when truncated to 160 characters. I also recommend tweaking the alarm description a bit to make it more meaningful. You might be able to use parameters in the alarm description, and then put that at the start of the Subject line.
Then at least the important information should get through, and it won't matter if the stuff at the end of the email body gets truncated.