Don’t get confused when you start playing with Exchange 2013
There are no send connectors created by default in 2013, although there is a receive connector configured to accept emails from the internet. When you do go ahead with creating a new send connector, the wizards are all the same, as in Exchange 2010.
Give a name to the send connector and choose “Internet” as the type.
Use MX record or route through a smart host if you have one.
Configure the address space, * if it is for all domains.
Click the “+” button to add the source servers for the connector.
You may get confused here, but it is the 2013 mailbox servers which will be sending the emails out. You can proxy the emails via the CAS servers if you so wish. If not, it will be the transport service on the mailbox server that makes the connection to the next hop, be it your smart host or the external mail server.
Select your mailbox servers and click Finish. You can now send emails to the internet