On Exchange 2013...

Can someone explain why on CAS servers by default there is a recieve connector on port 25?

The releationship between front end / back end IIS

http://blogs.technet.com/b/exchange/archive/2013/01/25/exchange-2013-client-access-server-role.aspx

It's still used as the front end transport service. You can view the transport architecture below.

below.

http://blogs.technet.com/b/rischwen/archive/2013/03/13/exchange-2013-mail-flow-demystified-hopefully.aspx

Hi,

Port 25 in Exchange 2013 just like in previous versions of Exchange is used for SMTP. Used by both External SMTP into the Front End Transport Service (FET), SMTP with Exchange 2007\2010 hub servers, between MBX servers, and also from the FET to the Transport Service. There is a receive connector named Default Frontend <servername> that listens on this port.

Front End Transport service runs on all Client Access servers and acts as a stateless proxy for all inbound and outbound external SMTP traffic for the Exchange 2013 organization. The Front End Transport service doesn't inspect message content, only communicates with the Transport service on a Mailbox server, and doesn't queue any messages locally. For more information about Exchange 2013 mail flow, please refer to:

http://blogs.technet.com/b/rischwen/archive/2013/03/13/exchange-2013-mail-flow-demystified-hopefully.aspx

Regards,

My next question then is...what is the point of proxying SMTP through CAS why not just deliver to the MBX servers?

also on the front end transport service in the diagram above what is the arrows between SMTP receive & SMTP send for inbound or is this howing outbound from SMTP send on the transport service? (although there are 2 lines one red and one purple....)