[Dovecot] using %d in passdb

hi,

i'd like to seperate the password file for seperate virtual domains into seperate files. i tried specifying:

passdb = passwd-file /etc/exim_incoming/local/accounts/pwdb/%d

but i get an error message that it couldn't open the particular file, and then Dovecot shuts down.

is there a way to do lazy-lookups?

or, would i be required to write a little helper program and have Dovecot connect to its socket to do auth?

leon