smtp - Exchange 2013 Internal Relay via Smart Host

Thank you for your help in advance! I am currently setting
up an Exchange 2013 server, to replace our old POP3/SMTP system, however we would like
to roll this out gradually when convenient for our
staff.

Our plan is
therefore:

• Setup Exchange
  2013 to retrieve email via POP Connector -
  Done


• Setup Exchange 2013 to send
  ALL mail via a SmartHost -
  Issues

I
have set the domains in Mail Flow > Accepted Domains to Internal Relay, enabled a
Smart Host for * as the domain name, and disabled/deleted the accounts that are not
setup yet; however Exchange just bounces the emails with no
errors.