show error page for not existing subdomain

The scenario:

- registered subdomains list
sub1.domain.com
sub2.domain.com
sub3.domain.com

Someone tries to hit sub4.domain.com which doesn't exists.
There's a wildcard record on the external nameserver so every unknown domain will hit main domain showing imscp login form.

There's a way to show an error page when an http/s request is trying to hit a subdomain which doesn't exists?

Maybe this is what I'm looking for
http://forum.i-mscp.net/Thread…OGRESS-Secure-admin-panel

Quote from redcloud

Maybe this is what I'm looking for
http://forum.i-mscp.net/Thread…OGRESS-Secure-admin-panel

I solved in an elegant way adding this line

ServerAlias *.mydomain.com

into /etc/apache2/imscp/mydomain.com.conf file

Now, every not existing subdomain will hit mydomain.com
which does not solve part of my problem (show an error page) but it's a decent solution