[exim] dsearch doesn't work

Hi.

I'm trying to replace my local_domains file with a dsearch lookup because I
also have a directory that contains a file for each domain (for other
reasons). This way, I could save the redundant file.

Unfortunately, I get the following, even though the file exists and I
already checked the permissions of the directory:

# exim4 -d -bt user@???
...
local_part=mail domain=example.org
checking domains
example.org in "@:localhost:dsearch:/var/www/vhost/"? no (end of list)

(I wonder why there is "dsearch:" instead of "dsearch;", but the colon is
also there with lsearch which works, so that shouldn't be of harm.)

dsearch is contained in the list of lookup types.

Do you have any ideas?
Thanks!

Peter