Limit outgoing SMTP connections

[and...@sh3.com.br]

I have a Postfix Server configured by myself running on a 3rd part linux 
cloud server.

This cloud server __has__ to be limited to up to 60 SMTP outgoing 
concurrent connections at the once. If it bypass this limit, it's 
blocked for 30 minutes and the postfix can't deliver any e-mail during 
this interval. There's no limit receiving e-mails.
Mails sent from virtual transport don't affect ths rule.
The question is: How can I limit Postfix (Smtp, Queue, ...) to make up 
to X SMTP outgoing concurrent connections?

I already tryed:

master.cf
---------
smtp    unix  -       -       -       -       X       smtp
        -o smtp_destination_concurrency_limit=Y

I suppose that the max number of concurrent connections will be X * Y, 
so in my conf X = 1 and Y = 10. But it is still relaying more than 60 
connections at once. Where I'm wrong?

Thanks in advance;
    Andrey