I recommend you to following:
Go to the document root of Roundcube (webmail):
cd /usr/local/cwpsrv/var/services/roundcube
create a simple php file:
echo "<?php phpinfo(); ?>" > aa.php
chown cwpsvc.cwpsvc aa.php
then try to access it over the web (in your browser):
http://hostname.com/webmail/aa.phpif you get the error 403 again then most likely the problem is caused by wrong user/group, access permissions or .htaccess file.
Make sure the folder of roundcube belongs to
cwpsvc:cwpsvc
All folders have access permissions 755 (rwx-rx-rx) and files 644 (-rw-r--r--) except
config/config.inc.php 640 (rw-r-----)
If the access permissions (ownger:group, etc) are correct then rename .htaccess to something like .htaccess_backup and try to access the file aa.php over the web again. In case it can be accessed then investigate your .htaccess.
Don't forget to remove the file aa.php when all test are finished.