[Dovecot] Thunderbird got "Mail Server does not support secure authentication" ???

[Adrian Mak]

System: Redhat AS3
postfix 2.2.5
cyrus-sasl 2.1.15
pam-mysql 0.6
dovecot 0.99.14 ( compile from source tarball)

The same email account and machine, using thunderbird 1.06 to get
email thru dovecot pop3, it returned "Mail Server does not support
secure authentication"
But in outlook express , there is no such problem

I have tested SASL thru pam-mysql is work properly before install dovecot
Below is my dovecot.conf

/etc/dovecot.conf
base_dir = /var/run/dovecot/

protocols = imap pop3
imap_listen = *
pop3_listen = *

ssl_disable = yes

login = imap
login = pop3

login_dir = /var/run/dovecot-login

login_executable = /usr/local/libexec/dovecot/imap-login
login_executable = /usr/local/libexec/dovecot/pop3-login

imap_executable = /usr/local/libexec/dovecot/imap
pop3_executable = /usr/local/libexec/dovecot/pop3

disable_plaintext_auth = no
login_user = dovecot

first_valid_uid = 1000
last_valid_uid = 1000

valid_chroot_dirs = /var/spool/virtual

default_mail_env = /var/spool/virtual/%u

auth = default
auth_mechanisms = plain
auth_userdb = mysql /etc/dovecot/mysql.conf
auth_passdb = mysql /etc/dovecot/mysql.conf
auth_executable = /usr/local/libexec/dovecot/dovecot-auth
auth_user = dovecot-auth

/etc/dovecot/mysql.conf
db_host = localhost
db_port = 3306
db_unix_socket = /tmp/mysql.sock
db = postfix
db_user = postfixuser
db_passwd = userpostfix
db_client_flags = 0

password_query = SELECT password FROM mailbox WHERE username = '%u'
user_query = SELECT maildir, 1000 AS uid, 1000 AS gid FROM mailbox
WHERE username = '%u'