Google Outbound Services Configuration Guide - Manual (Page 128)

Postfix 139
2. Restart Postfix by running the following command:
# sudo postfix reload
Test Outbound Mail
Check the mail queues of the mail server.
1. In the Internet Mail Service Properties select the Queues tab. Look for items
with a retry state which could indicate outbound mail delays.
2. Send a message from a mail client inside your network to an outside address.
You should see a line in the header email which indicates being received and
delivered by
exprodNobM.obsmtp.com , where N and M are numbers.
3. Test inbound mail to confirm normal functionality. Send a message from an
outside email address to an address on your service.
4. Confirm that your mail server is not an open relay. An open relay will make
your mail server vulnerable to hijacking from spammers and will most likely
cause an interruption in service.
Use an external open relay test, such as http://www.mxtoolbox.com/
diagnostic.aspx or http://www.spamhelp.org/shopenrelay/ . If the result
shows that you have an open relay, correct your private relay settings. If you
see an uncertain response (such as “maybe” or “warning”) then check that
your private relay settings are correct.
See “Set Up Reinjection” on page 138 for the correct private relay settings.