dovecot - Dec 2006 - vpopmail problem

Hi! Sorry for my english...

I recently know about dovecot and I try to use it on my server.
Previously I used qmail+vpopmail+courier and now I want to use
postfix+dovecot and, to mantain all my mailboxes structure, I try to
use dovecot with vpopmail.

During configuration the script detects my vpopmail installation and
configuration and after I get this status:
Install prefix ...................... : /usr/local
File offsets ........................ : 64bit
I/O loop method ..................... : poll
File change notification method ..... : dnotify
Building with SSL support ........... : yes (OpenSSL)
Building with IPv6 support .......... : yes
Building with pop3 server ........... : yes
Building with mail delivery agent  .. : yes
Building with GSSAPI support ........ : no
Building with user database modules . : static prefetch passwd
passwd-file checkpassword vpopmail (modules)
Building with password lookup modules : passwd passwd-file shadow
checkpassword vpopmail (modules)

And after some testing I start the daemon with this config:
protocols = imap imaps pop3 pop3s
auth default {
  mechanisms = plain
  passdb vpopmail {}
  userdb vpopmail {}
  user = vpopmail
}

I connect to localhost via pop3 and when I try to auth some user I get  this:

Dec 26 01:27:45 anet dovecot: auth(default): client in: AUTH       1
    PLAIN   service=IMAP    secured lip=127.0.0.1   rip=127.0.0.1
 resp=AHNyb2RvbkBncmFjaWFuZXQub3JnAHR3aXN0
Dec 26 01:27:45 anet dovecot: auth(default):
vpopmail(srodon at anet.org,127.0.0.1): unknown user
Dec 26 01:27:46 anet dovecot: auth(default): client out: FAIL      1
    user=srodon at anet.org
Dec 26 01:27:46 anet dovecot: imap-login: Aborted login:
user=<srodon at anet.org>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1,
secured

I tried other auth methods but I get an "Unsupported authentication
mechanism" error. A try with encrypted password files and with a plan
one.

thanks in advance!