[Dovecot] newbie: can't login as virtual user

[sean darcy]

dovecot -n
# 2.0.15: /etc/dovecot/dovecot.conf
# OS: Linux 2.6.38.8-32.fc15.i686.PAE i686 Fedora release 15 (Lovelock)
auth_debug_passwords = yes
disable_plaintext_auth = no
info_log_path = /var/log/dovecot-info.log
log_path = /var/log/dovecot.log
mail_access_groups = mail
mail_location = mbox:~/mail:INBOX=/var/spool/mail/%u
mail_privileged_group = mail
mbox_write_locks = fcntl
passdb {
   args = username_format=%u /etc/dovecot/users
   driver = passwd-file
}
service lmtp {
   unix_listener /var/spool/postfix/private/dovecot-lmtp {
     group = postfix
     mode = 0666
     user = postfix
   }
}
ssl_cert = </etc/pki/dovecot/certs/dovecot.pem
ssl_key = </etc/pki/dovecot/private/dovecot.pem
userdb {
   driver = passwd
}
userdb {
   args = username_format=%u /etc/dovecot/users
   driver = passwd-file
}
protocol lmtp {
   mail_plugins = quota sieve
}

cat /etc/dovecot/users
..........
test1 at example.com:{PLAIN}test1pass

BUT,
. OK Pre-login capabilities listed, post-login capabilities have more.
a login test1 at example.com test1pass
* BYE Internal error occurred. Refer to server log for more information.
closed

 From the server:
Oct 22 21:45:53 auth-worker: Debug: passwd-file /etc/dovecot/users: Read 
5 users
Oct 22 21:45:53 auth-worker: Debug: pam(test1 at example.com,www.xx.yy.zz): 
lookup service=dovecot
Oct 22 21:45:53 auth-worker: Debug: pam(test1 at example.com,  ): #1/1 
style=1 msg=Password:
Oct 22 21:45:55 auth-worker: Info: pam(test1 at example.com,   ): unknown user
Oct 22 21:45:55 auth: Debug: passwd-file(test1 at example.com,    ): 
lookup: user=test1 at example.com file=/etc/dovecot/users
Oct 22 21:45:55 auth: Debug: client out: OK	1	user=test1 at example.com
Oct 22 21:45:55 auth: Debug: master in: REQUEST	2303328257	27060	1 
964b20421c19356f1cbdefbf976467e0
Oct 22 21:45:55 auth: Debug: passwd(test1 at example.com,    ): lookup
Oct 22 21:45:55 auth: Info: passwd(test1 at example.com,   ): unknown user
Oct 22 21:45:55 auth: Debug: passwd-file(test1 at example.com,    ): 
lookup: user=test1 at example.com file=/etc/dovecot/users
Oct 22 21:45:55 auth: Debug: master out: USER	2303328257	test1 at example.com
Oct 22 21:45:55 imap-login: Info: Login: user=<test1 at example.com>, 
method=PLAIN, rip=   , lip=    , mpid=27062, TLS


What's wrong with my configuration?

Thanks,

sean