the Version 2.10 is not 2.1 !
To send E-Mails through external servers you have to setup a relay. Configuring through postconf is not recommended (at the next Zimbra restart and on upgrades the settings are overridden).
You can set your postconf settings through:
zmlocalconfig -e postfix_<postconf_variable_name>=<value>
Heres an example how to send E-Mails through external relays. They are not send over TLS but it might be a beginning:
In the Zimba Settings at the user account allow him only to send e-mails from the given accounts and add the external e-mail addresses.
Then goto the serversettings in the MTA Tab and disable DNS lookups.
For the next steps you have to login to your server as user zimbra.
Now run the following command:
In the next step you need a relayhost mapping.
zmprov mc default zimbraSmtpRestrictEnvelopeFrom FALSE
Create a config file for the maps, e.g. /opt/zimbra/conf/relayhost_map
In this file list the e-mail addresses and the external servers. One E-Mail address per line:
The next config file is for authentication. e.g. /opt/zimbra/conf/relay_password
In this file list the e-mail addresses with their usernames and passwords. One E-Mail address per line:
The next step is to configure postfix to send through external relays. Since Zimbra8 postconf settings were overridden on the next restart so you have to set these settings through Zimbra.
These are the needed commands:
Now you have to create the database files for the relay map files. You have to run this commands everytime you change relayhost_map or relay_password:
zmlocalconfig -e postfix_smtp_sender_dependent_authentication=yes
zmlocalconfig -e postfix_sender_dependent_relayhost_maps=hash:/opt/zimbra/conf/relayhost_map
zmlocalconfig -e postfix_smtp_sasl_auth_enable=yes
zmlocalconfig -e postfix_smtp_sasl_password_maps=hash:/opt/zimbra/conf/relay_password
zmlocalconfig -e postfix_smtp_cname_overrides_servername=no
zmlocalconfig -e postfix_smtp_use_tls=no # maybe setting this to yes for TLS?
zmlocalconfig -e postfix_smtp_sasl_security_options=noanonymous
Now you can reload/restart Zimbra to enable this configuration
The last step is to configure personalities at the Zimbra Frontend where you can add external POP3/IMAP Accounts.
Now you can send E-Mails through remote SMTP Servers.
Would be a nice idea for Zimbra 9 to directly integrate the ability to send e-mails from external servers.