Hi Everyone,

I'm hoping others on this forum have some thoughts on whether it is worthwhile deploying only the Exchange 2013 CAS role for the purposes of SMTP relay.

When using Exchange Online, most guides suggest installing the IIS virtual SMTP component in an environment if SMTP relay is required. This is simple enough, however Microsofts future plans for IIS vSMTP look uncertain.

So my question is, has anyone deployed only the Exchange 2013 CAS role in an environment solely for the purposes of SMTP relay?
One pitfall I'm thinking about is the autodiscover service. Once the CAS role is installed an AD SCP is created, so this could cause potential problems.

I'm not concerned about having to extend the AD schema, or the cost. It's the other technical bits :)

cheers!

Hi Peter, 

According to the document by Microsoft, Client Access and Mailbox server roles are required in your on-premises Exchange organization.
The Client Access server also handles all secure mail messages sent between the on-premises and the Exchange Online organizations, as well as handling transport rules, journaling policies, and message delivery to user mailboxes in a hybrid deployment. Also it host so many services, including calendar free/busy information sharing, message tracking, and mailbox moves between the on-premises and Exchange Online organizations.
The Mailbox server role hosts the on-premises recipient mailboxes and communicates with the Exchange Online organization by proxy via the on-premises Client Access server.
More details about Exchange Server 2013 Hybrid Deployments, for your reference:
https://technet.microsoft.com/en-us/library/jj200581(v=exchg.150).aspx

Best Regards,
Allen Wang

Hi Allen,

Thanks for the reply. I'm not completely sure it answers my question, as we are considering only having Exchange online, not a hybrid deployment.

The purpose of the onsite CAS was *only* to relay SMTP traffic, not proxy client communications.
I think I might stick with IIS for SMTP relay, rather than complicating things with the Exchange CAS role.


cheers!

Hi Peter-M, a CAS without a Mailbox Server doesnt work.

The CAS server would proxy the SMTP connection to a Mailbox Server.

regards,

daniel