subdomain problem

I created a subdomain , but I can not point it .
subdomain is : mail.dominio.it
why
created and put as the folder public_html\mail 

I put an index.html but  is wrong . why?

# vhost_start mail.sihost.it
ServerName mail.sihost.it
ServerAlias www.mail.sihost.it
ServerAdmin nikeddy@gmail.com
DocumentRoot "/home/sihost/public_html/mail/"
ScriptAlias /cgi-bin/ /home/sihost/public_html/mail//cgi-bin/
#
# Custom settings are loaded below this line (if any exist)
# Include "/usr/local/apache/conf/userdata/sihost/mail.sihost.it/*.conf

<IfModule mod_suexec.c>
        SuexecUserGroup sihost sihost
</IfModule>

<IfModule mod_suphp.c>
        suPHP_UserGroup sihost sihost
</IfModule>

<Directory "/home/sihost/public_html/mail/">
        AllowOverride All
</Directory>

</VirtualHost>
# vhost_end mail.sihost.it


but i link mail.sihost.it but not see my index.html but test page.

why?