Where is apache plugin getting this domain from?

[_az]

@Osiris

Apache doesn't just come up with that hostname. It has to come from somewhere in that configuration file.

It can, if there is no ServerName and the VirtualHost contains a bind address that Apache can turn back into a domain name:

If no ServerName is specified, the server attempts to deduce the client visible hostname by first asking the operating system for the system hostname, and if that fails, performing a reverse lookup on an IP address present on the system.

Pretty crappy behavior; just use ServerName.

edit: better citation