How to control access for specific IP-addresses of clients when using as mail proxy

[mikiso]

Finally I wrote mail access module with reference to the source code of
http access module and 
Evan Miller's guide to Nginx module development because we need this
feature for only pop3 proxy.

And I noticed I don't understand how my module to be called before the
pop3 handler.
>From the guide it is important the order of the modules, however it
doesn't mention granular control
 for request/connection handling.

So I'd like to know how to call this handler before the pop3 handler and
how the ngx_mail_pop3_init_session is 
called after "epoll_process_event".

Do I need to register connection handler or do I need to implement tcp
based source code as he does?

Regards,
Soichiro

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,216892,216979#msg-216979