Please Help me!

[Asdsl]

Hi World,
Here is my new Linux Problem:

My RedHat 8 with Apache and PHP, is working. Now I have a little problem:
I did install Squireelmail, and it’s working Ok.
I did connect it to my local Network and it’s working too. When I try to get the Webmail from other computer in my Network I can’t reach my Webmail with the Host Name.

How may I fix it?

Example:

My Host Name = mail.agstek.com
Domain agstek.com
Local IP = 192.168.65.5

In my Linux box I can reach it with:
http://mail.agstek.com/webmail/index.php

I’d like to reach it from any other win PC in my local network via browser.
Now I only can reach it with:
http://192.168.65.5/webmail/index.php
Is it possible?
How?
What do I have to do?

Thanks in advance!