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.