I've now found the folder /ect/psa-webmail/roundcube
I edited the roundcube.conf file, as to contain the correct Docroot path.
After a reboot, still no redirect.
Stangely there is a roundcube_vhost.conf file in the folder, none of the other webmail clients have one.
So how did it get there?
I try removing it but still no joy.
Any help would be much appreciated.