I am using 1and1 cloud with plesk.
I have a http://primary.com and an http://addon.com
Right now if if some one enter any none existing subdomain e.g. blabla.addon.com, the URL in browser address bar stays the same but contents coming from http://primary.com/
I wanted contents to come from http://addon.com
Can anyone please guide me to the right direction?
This happens because by default Plesk will serve it's "Web Server's Default Page" template.
If you want to change this behaviour you need to set a default domain that will be served instead.
The setting you are looking for is located at:
Tools & Settings > IP Addresses > Your IP (click) > Default site > Domain (addon.com)