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