"unknown user - trying the next userdb" Info in log

[James Brown via dovecot]

I’ve set up a new mail server. Auth-worker is giving me this error all the time:

auth-worker(11160): Info: passwd(sa...@bordo.com.au 
<mailto:sa...@bordo.com.au>,10.0.0.54,<YSFoAYHAGoLAqAEo>): unknown user  - 
trying the next userdb

Next line is from imap-login with successful login.

Using MySQL as user database.

Auth-sql.comf.ext is:

passdb {
  driver = sql

  # Path for SQL configuration file, see example-config/dovecot-sql.conf.ext
  args = /usr/local/etc/dovecot/dovecot-sql.conf.ext
}

# "prefetch" user database means that the passdb already provided the
# needed information and there's no need to do a separate userdb lookup.
# <doc/wiki/UserDatabase.Prefetch.txt>
userdb {
  driver = prefetch
}

userdb {
  driver = sql
  args = /usr/local/etc/dovecot/dovecot-sql.conf.ext
}

# If you don't have any user-specific settings, you can avoid the user_query
# by using userdb static instead of userdb sql, for example:
# <doc/wiki/UserDatabase.Static.txt>
#userdb {
  #driver = static
  #args = uid=vmail gid=vmail home=/var/vmail/%u
#}

Any ideas why it is gives me this error before logging in? Where should I look?

Thanks,

James.