[exim] appendfile allow_symlink

By default, appendfile will not deliver if the path name for the file is
that of a symbolic link. Setting the allow_symlink option relaxes that
constraint. Is there any way that I can get middle ground by enabling
"allow_symlink", but only allowing symlinks that are owned by say,
root/exim? I don't want a user to be able to delete my symlink of
/var/mail/USER to /real/path/of/var/mail.

Jason.