[问题]问个关于postfix配置的问题

[big]

我以前一直在deiban下用exim4+fetchmail+mutt,前段时间改了ubuntu,默认的好像是postfix,估计应该差不多的，但是一直配置不发不了信，
下面是我的main.cf文件和日志文件，大家帮忙看下什么地方的问题：
##########################main.cf#####################
See /usr/share/postfix/main.cf.dist for a commented, more complete version
# Debian specific: Specifying a file name will cause the first
# line of that file to be used as the name. The Debian default
# is /etc/mailname.
#myorigin = /etc/mailname

smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
biff = no

# appending .domain is the MUA's job.
append_dot_mydomain = no

# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h

# TLS parameters
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${queue_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${queue_directory}/smtp_scache

# See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for
# information on enabling SSL in the smtp client.

myhostname = titan-laptop
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
mydestination = titan-laptop, localhost.localdomain, , localhost
relayhost = smtp.21cn.com
mynetworks = 127.0.0.0/8
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all
myorigin = /etc/mailname
inet_protocols = all

#25 Dec add
smtpd_sasl_auth_enable = yes
smtpd_sasl_local_domain=
# 允许明文
smtpd_recipient_restrictions = permit_sasl_authenticated,permit_mynetworks,reject_unauth_destination
smtpd_client_restrictions = permit_sasl_authenticated
broken_sasl_auth_clients =yes
smtpd_sasl_security_options = noanonymous
smtp_sasl_password_maps = hash:/etc/postfix/saslpass
# smtp认证的密码文件
mailbox_command = procmail -a "$EXTENSION"

#####################end of main.cf###################

#######################log##########################

Dec 26 16:12:54 titan-laptop postfix/master[17661]: daemon started -- version 2.3.3, configuration /etc/postfix
Dec 26 16:13:27 titan-laptop postfix/pickup[17662]: 079F747028C: uid=1000 from=<lastmandancing@21cn.com>
Dec 26 16:13:27 titan-laptop postfix/cleanup[17708]: 079F747028C: message-id=<20061226081326.GA17690@21cn.com>
Dec 26 16:13:27 titan-laptop postfix/qmgr[17663]: 079F747028C: from=<lastmandancing@21cn.com>, size=421, nrcpt=1 (queue active)
Dec 26 16:13:27 titan-laptop postfix/smtp[17710]: 079F747028C: to=<titan_njupt@163.com>, relay=smtp.21cn.com[202.104.32.230]:25, delay=0.8, delays=0.05/0.01/0.63/0.11, dsn=5.0.0, status=bounced (host smtp.21cn.com[202.104.32.230] said: 553 lastmandancing@21cn.com: Sender address rejected: not logged in (in reply to MAIL FROM command))
Dec 26 16:13:28 titan-laptop postfix/cleanup[17708]: 02B8747028D: message-id=<20061226081328.02B8747028D@titan-laptop>
Dec 26 16:13:28 titan-laptop postfix/qmgr[17663]: 02B8747028D: from=<>, size=2287, nrcpt=1 (queue active)
Dec 26 16:13:28 titan-laptop postfix/bounce[17713]: 079F747028C: sender non-delivery notification: 02B8747028D
Dec 26 16:13:28 titan-laptop postfix/qmgr[17663]: 079F747028C: removed
Dec 26 16:13:33 titan-laptop postfix/smtp[17710]: 02B8747028D: to=<lastmandancing@21cn.com>, relay=smtp.21cn.com[202.104.32.230]:25, delay=5.6, delays=0.02/0/5.5/0.09, dsn=5.0.0, status=bounced (host smtp.21cn.com[202.104.32.230] said: 553 <null sender>: rejected,not allow null sender to send mail (in reply to MAIL FROM command))
Dec 26 16:13:33 titan-laptop postfix/qmgr[17663]: 02B8747028D: removed

################end of log#############################