I installed Zimbra 8.1 on Ubuntu 12.04.2 server LTS everything seems to be okay unless I changed the mta relay host to be use gmail.com, I applied the following parameters

echo mail.domain.com smtp.gmail.com admin@domain.com:1109 > /opt/zimbra/conf/relay_password
postmap hash:/opt/zimbra/conf/relay_password
postmap -q mail.domain.com /opt/zimbra/conf/relay_password
zmlocalconfig -e postfix_smtp_sasl_password_maps=hash:/opt/zimbra/conf/relay_password
zmlocalconfig -e postfix_smtp_sasl_auth_enable=yes
zmlocalconfig -e postfix_smtp_sasl_security_options=noanonymous
zmlocalconfig -e postfix_smtpd_use_tls=yes
zmlocalconfig -e postfix_smtp_cname_overrides_servername=no
zmlocalconfig -e postfix_smtp_tls_security_level=may
zmlocalconfig -e postfix_lmtp_host_lookup=native
zmmtactl restart
postfix reload
By I'm getting the following bounced back email

HTML Code:
host smtp.gmail.com[] said: 530-5.5.1
    Authentication Required. Learn more at 530 5.5.1
    http://support.google.com/mail/bin/answer.py?answer=14257 a9sm26174786wiv.0
    - gsmtp (in reply to MAIL FROM command)
Any help with this matter would be appreciated in advanced.