how to configure virtual smtp, server has horde, unable to send from external client

[peter....@glendiscovery.co.uk]

Hi
I have set up a RedHat 6 server with Horde 5, it works correctly now (after much headscratching) for users using imp for their mail.
However, if using an external mail client (I have been testing with thunderbird 17.0.4) -
I can send and receive messages from horde / imp to users on external domains and also I can send mail from Thunderbird to imp users on the server but not beyond to the external domains as the server will not act as a relay
postfix-2.6.6-2.2.el6_1.x86_64
Sasl appears to be running
00:00:00 /usr/sbin/saslauthd -m /var/run/saslauthd -a pam -r
Most of the howtos I have tried to follow assume a single local domain, but with virtualmin and horde one can have multiple domains. I have been through the dovecot howtos several times, trying to modify main.cf to permit relaying. I don't want any bells and whistles, just a configured main.cf which will allow this. The server currently has 24 domains configured, most of which will eventually require mail relay.
Users within horde can send and receive mail, between themselves and to and from external email addresses.
When I use thunderbird as an external client I can see the mail, but fails every time on smtp for sending.
The smtp setting in Thunderbird is STARTTLS with normal password
The error is "An error occurred sending mail: The mail server sent an incorrect greeting: "
If I use my google smtp setting it works.
I have spent hours trying to follow:
http://www.postfix.org/documentation.html
http://www.postfix.org/BASIC_CONFIGURATION_README.html

Here is the code I have added to /etc/postfix/main.cf
the virtual file and virtual.db contain all the domains and users, postmap -q seems to give the correct responses.
I don't have a vmailbox

virtual_alias_maps = hash:/etc/postfix/virtual
virtual_mailbox_domains = $virtual_mailbox_maps
# virtual_mailbox_maps = hash:/etc/postfix/vmailbox
virtual_mailbox_base = /var/mail
virtual_uid_maps = static:5000
virtual_gid_maps = static:5000
sender_bcc_maps = hash:/etc/postfix/bcc
mailbox_command = /usr/bin/procmail-wrapper -o -a $DOMAIN -d $LOGNAME
home_mailbox = Maildir/
broken_sasl_auth_clients = yes
mailbox_size_limit = 0
allow_percent_hack = no
smtpd_sasl_authenticated_header = yes

smtpd_recipient_restrictions = permit_sasl_authenticated permit_mynetworks check_relay_domains
# inserted pjl for SASL
smtpd_sasl_path = smtpd
smtpd_sasl_tls_security_options = %smtpd_sasl_security_options
smtpd_sasl_local_domain = $myhostname

# SASL SUPPORT FOR SERVERS
#
# The following options set parameters needed by Postfix to enable
# Cyrus-SASL support for authentication of mail servers.
#
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options =
allow_untrusted_routing = yes