Thanks for reply. I did. Here is what i did

===================

<VirtualHost *:80>
    ServerAdmin webmaster@dummy-host.example.com
    DocumentRoot /var/www/roundcubemail/
    ServerName mail.my-domain.com
</VirtualHost>

<VirtualHost *:80>
    ServerAdmin webmaster@dummy-host.example.com
    DocumentRoot /var/www/html/
    ServerName my-domain.com
</VirtualHost>

<VirtualHost *:80>
    ServerAdmin webmaster@dummy-host.example.com
    DocumentRoot /var/www/iredadmin/
    ServerName iredadmin.my-domain.com
</VirtualHost>

===========

When i go mail.my-domain.com. It auto redirected to mail.my-domain.com/mail
When i go my-domain.com. It auto redirected to my-domain.com/mail
When i go iredadmin.my-domain.com. It redirected to Default Apache Site.

I think there is another configuration for this. Not only create Virtual host ...

Thanks. I remove index.html file
Now i can access mail.my-domain.com without being autoredirected to mail.my-domain.com.mail
How i can turn off HTTPS for iredadmin? and what is exactly DocumentRoot for Iredadmin for setting Virtual hosts?

Indeed! Reading this, I also want to say that you don't want to turn off HTTPS.
Even better is to redirect everything on 80 to 443.

Nice idea of using iredmail.domain.com instead of www.domain.com/iredmail
But then you need a A record in DNS and thus can be lookup easy.
As the ireadadmin interface uses UID and password, it could that you are a target for hackers.
What I would do in this kind of situations is using exta logins with htaccess. Yes the you have to log in twice,
but makes it harder to directly attack the application.

If you only connect from the same source, then use rules in the virtual host, order allow deny, that stuff.
And configure that only your IP can connect.

Well, just my thoughts. Trying to secure some things.

Why not check /etc/httpd/conf.d/ssl.conf for example?
Addition tutorial: http://httpd.apache.org/docs/2.2/mod/mod_ssl.html