[Dovecot] dovecot-lda and sieve filtering (SMTP is Postfix)

[Der Olli]

Hello list.
I've got a working Dovecot with Postfix and MySQL-support but everything 
from the capabilities of sieve isn't working except one thing: Sorting 
emails to folders works fine. But no vacation, no reject, no redirect. I 
don't get any errors in the logs. Verbose logging is enabled.
I compiled both from newest cvs-sources but also tried older 
combinations (nightly snapshots). Always the same result and there's no 
.dovecot.sieve.err so script is okay. If it is not, .dovecot.sieve.err 
will be generated. I've tested this :)
Anyone here who has a working sieve implementation with dovecot-lda? 
Where do I have to search? Is it a configuration problem? Where can I 
configure which sending mechanism dovecot-lda should use? Is it a local 
sendmail binary? Where does dovecot-lda search for it. Is it a 
SMTP-server? So there's one on port 25 at the local machine.

Greetz, Olli