[Dovecot] local delivery agent

[legionaer85]

Hey, i've got a problem with my lda and exim, probably i assume that 
it's dovecot.
I think that, because i get an error in exim:
T=dovecot_delivery: Child process of dovecot_delivery transport returned 
67 (could mean user nonexistent) from command: /usr/lib/dovecot/deliver
in exim i use /usr/lib/dovecot/deliver -d <name>@<domain>.<tld> -f 
<name>@<domain>.<tld>

So, i tried to focus the error and thought there is not the right 
argument for delivery. But i couldn't get any hints about the arguments 
for the deliver agent.
Exim gives me a complete string which is 'name at domain.ltd'
Now my question. How parses the deliver agent this string? Splits it 
into variables? If yes... to which ones? name and domain?

Thanks a lot for any answers.

=>dovecot --version
1.0.rc15
------
=>dovecot -n
# /etc/dovecot/dovecot.conf
log_path: /var/log/dovecot/main.log
info_log_path: /var/log/dovecot/info.log
log_timestamp: %Y-%m-%d %H:%M:%S
ssl_cert_file: /etc/ssl/certs/ssl_cert.crt
ssl_key_file: /etc/ssl/certs/ssl.key
login_dir: /var/run/dovecot/login
login_executable: /usr/lib/dovecot/imap-login
login_user: vmail
login_greeting: <servername> Mailserver ready.
verbose_proctitle: yes
first_valid_uid: 8
last_valid_uid: 8
mail_privileged_group: mail
mail_location: dbox:/var/spool/mail/%d/%n
mail_debug: yes
auth default:
  user: mail
  passdb:
    driver: sql
    args: /etc/dovecot/dovecot-sql.conf
  userdb:
    driver: prefetch
  socket:
    type: listen
    client:
      path: /var/run/dovecot/auth-client
      mode: 384
      user: mail
      group: mail
    master:
      path: /var/run/dovecot/auth-master
      mode: 384
      user: mail
      group: mail
---------
=>grep -v '^ *\(#.*\)\?$' /etc/dovecot/dovecot-sql.conf
driver = mysql
connect = host=<host> dbname=<dbname> user=<user> password=<pass>
default_pass_scheme = PLAIN
password_query = SELECT password, '/var/mail/%d/%n' AS userdb_home, 
'mail' AS userdb_uid, 'mail' AS userdb_gid FROM user WHERE username = 
'%n' AND domain = '%d' AND IMAP_allowed = 'YES'
user_query = SELECT username, uid, gid FROM user WHERE username = '%n' 
AND domain = '%d'
---------
in the db i have the user table columns: username, domain, password