Reciving Email in exchange 2003

hey guys…i never set up exchange before and i read a few articles of off google and set it up……i can send email but i can not recive any email…
I also activated the pop3 service in services in my server but nothing i also think i set up my mx records..right..can ya verify?
i use yahoo
so the A record goes to mail.mysite.net then its fowared to my IP
and my mx record is mail.mysite.net
is this right???
or is there a good article on this?
and what good security can i set becuase i dont want my passwords in clear text and becuase am planning on doing it on https also so the employess can access from the internet