I can't speak to that. All of my organizations that use it have under 10 users, and I moved them over back when "organizations with fewer than 10 users" were free.
What I can say, though, is that you basically specify the catch-all to go to one user.
So you would have drew@htclyg.com, and mike@htclyg.com. Those are two separate accounts. Drew doesn't see Mike's email, and the opposite is also true. Then you set up the catch-all to go to Drew. Drew will now see any-email-address-here-except-mike@htclyg.com. Mike will only see email to mike@htclyg.com.
Make sense?
-Mike
@MikeVitale42
"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety."
- Benjamin Franklin, 1759 Historical Review of Pennsylvania