Heres my suggestion:
When your computer Is IDLE (not away actually idle), toasts will still popup, but when you get back and move your mouse, or whatever you do to wake your computer up, any toasts you missed will popup, not "Someone said hi", or "Has just signed in" but things like...
"Person 3 has just sent you an email"
"Person 2 has just sent you an email"
"Person 1 has just sent you an email"
And other important toasts, because Instead of going and checking on the main window how many emails you have, it will just make toasts for all the ones you missed.
Like Comeback Toasts, actually Comeback Toasts would be a toast when a friend logs in, which is a basic Messenger Feature so...