On my new i3 setup I got no notifications of new MCabber events and messages.

The regular alerts from MCabber did not work with terminator.

Therefore I created a custom event script (set events_command), wich simulates an alert on the terminal window with mcabber:

#!/bin/bash
wmctrl -r "mcabber" -b add,demands_attention

With this configuration I get a red workspace indicator when a message arrives.