I wanted to be notified when there's new mail in my inbox which is a standard Maildir synced via mbsync. My setup is i3wm with a dedicated mutt workspace and $mod-m to change to the "mail" workspace and launch a mutt instance. I managed to mark the workspace "urgent" via a named pipe running as background process in the same terminal window as mutt. See all the details here: https://gist.github.com/niko/7816377
I'm almost happy with the setup. Sometime I have to manually redraw the mutt screen. I think mutt gets confused by the background process writing the bell command.
What do you think?
I don't know about the blinking LED part, but I was kind of amazed to see my i3 workspace marked as urgent when I started using termite. I never really cared enough to try to figure it out (nor did I even think about it to be honest), but it doesn't do this for me with urxvt.