[Dovecot] Strange error: DIGEST-MD5 mechanism can't be supported with given passdbs

[Yubao Liu]

Hi all,

I have no idea about that message, here is my configuration, what's wrong?
Debian testing, Dovecot 2.0.15

$ doveconf -n
# 2.0.15: /etc/dovecot/dovecot.conf
# OS: Linux 3.1.0-1-686-pae i686 Debian wheezy/sid
auth_default_realm = corp.example.com
auth_krb5_keytab = /etc/dovecot.keytab
auth_master_user_separator = *
auth_mechanisms = gssapi digest-md5
auth_realms = corp.example.com
auth_username_format = %n
first_valid_gid = 1000
first_valid_uid = 1000
mail_location = mdbox:/srv/mail/%u/Mail
managesieve_notify_capability = mailto
managesieve_sieve_capability = fileinto reject envelope 
encoded-character vacation subaddress comparator-i;ascii-numeric 
relational regex imap4flags copy include variables body enotify 
environment mailbox date ihave
passdb {
  args = /etc/dovecot/master-users
  driver = passwd-file
  master = yes
  pass = yes
}
passdb {
  driver = pam
}
plugin {
  sieve = /srv/mail/%u/.dovecot.sieve
  sieve_dir = /srv/mail/%u/sieve
}
protocols = " imap lmtp sieve"
service auth {
  unix_listener auth-client {
    group = Debian-exim
    mode = 0660
  }
}
ssl_cert = </etc/ssl/certs/dovecot.pem
ssl_key = </etc/ssl/private/dovecot.pem
userdb {
  args = home=/srv/mail/%u
  driver = passwd
}
protocol lmtp {
  mail_plugins = " sieve"
}
protocol lda {
  mail_plugins = " sieve"
}

# cat /etc/dovecot/master-users
x...@corp.example.com:zzzzzzzz

The zzzzz is obtained by "doveadm pw -s digest-md5 -u x...@corp.example.com",
I tried to add prefix "{DIGEST-MD5}" before the generated hash and/or add
"scheme=DIGEST-MD5" to the passwd-file passdb's "args" option, both 
don't help.

The error message:
dovecot: master: Dovecot v2.0.15 starting up (core dumps disabled)
dovecot: auth: Fatal: DIGEST-MD5 mechanism can't be supported with given 
passdbs
gold dovecot: master: Error: service(auth): command startup failed, 
throttling

I opened debug auth log,  it showed dovecot read /etc/dovecot/master-users
and parsed one line, then the error occurred.  Doesn't passwd-file 
passdb support
digest-md5 password scheme?  If it doesn't support, how do I configure 
digest-md5 auth
mechanism with digest-md5 password scheme for virtual users?

Regards,
Yubao Liu