Help needed for my first mail server

[Jason Hsu <jhsu802701@jasonhsu.com>]

This is my first time ever working with a mail server.  Thus, I don't know what I'm doing, but I'm trying to learn.  

All I'm trying to do right now is send and receive email messages through my free DynDNS account.  Let's say it's subdomain1.dyndns-free.com .

The OS is Debian Lenny.  The mail server is exim4.

Let's say that the host name listed in my /etc/hosts file is subdomain2.domain.com .

I have been able to run the exim4 configuration script by entering "dpkg-reconfigure exim4-config".  However, I don't know what I'm supposed to enter for all those fields I'm asked about.  If I'm even slightly wrong on just one thing, my system won't work properly.

Do I need an MX hostname?  There are so many unknowns that I don't know where to begin.

-- 
Jason Hsu <jhsu802701@jasonhsu.com>