Apache mod_macro gets configured with a ServerAlias for a subdomain of the domain name of this server. The idea is to have development hostnames that you can use before updating DNS when migrating existing sites. Check the ServerAlias configs in /etc/apache2/mods-available/macro.conf to make sure they are using the domain you wish, and optionally change or comment out the subdomain ServerAlias settings.
The default website page is /srv/www/html/index.html. You can edit this page to suit your needs. This default page is displayed for any domain that points to the server, but has not been enabled as it's own VirtualHost yet.
If you just want a minimal smtp mail server for getting automated emails (cron, website contact forms, etc.) off the server you can install and configure exim4-daemon-light with the commands below. Note if you started with base-stack this has already been done.