Hi Hajo,

Look for this in Web.config and set it to true (or put it in user.config and set it to true)

<!--
AllowForcingPreferredHostName, if set to true a new Site Setting appears (only in root site or IsServerAdminSite)
for entering a preferred host name. The reason this is disabled by default and only available from within the
server admin site is because putting an invalid host name in this site setting can make the site inaccessible
as it will keep redirecting to an incorrect host name. So this is only for expert use, but is useful in cases where
you may have a site that responds to multiple host names like mojoportal.org, mojoportal.com, www.mojoportal.com
and you want to always force a specific one. For example, my ssl certificate only matches www.mojoportal.com
so I want to force the sue of that host name by redirecting to it if a request comes in for a different host name.
-->
<add key="AllowForcingPreferredHostName" value="false" />

See the comments to understand why its not enabled by default. After you set that to true the preferred host setting shows up in Site Settings.

Best,

Joe