Exchange – Single public IP address and easy SMTP High availability

This article is about use high availability of very simple kind, when you have single public IP address without possibility to forward traffic to more than one hosts. In my case I have single public IP address in my LAB, I use Steve Goodman´s Exchange 2010 HAProxy (, which is not compiled for SMTP traffic. I have 2 node Exchange 2013 DAG with CAS/MAILBOX roles on each node.
This configuration simply means, that I cannot use Win NLB, because DAG cannot operate on the same machine as Win NLB does.


I used single node to route SMTP traffic to and in case of node failure SMTP traffic was held on gateway till the node came up.

Current setup

Well. If I think about DAG itself, it is high available cluster solution for Exchange 201x. For me there are 2 aspects good for SMTP high availability:

  • DAG has its own IP address
  • IP address is assigned to node running Active Manager and quorum

Yes, these 2 things are essential. If I route SMTP traffic to DAG IP, I will have it allways online and available, because if Active Manager is not online and accessible on single DAG node, DAG is in serious problems and most probably some or all databases will not work.

What to do to make it work?

  • On each DAG node create new internet receive connector bound to Frontend Transport Service, which is stateless SMTP proxy (running on Client Access role), routing traffic to Transport Service on Mailbox server role. Bind the connector to DAG IP address.

New-ReceiveConnector -Name “From Internet” -Bindings “” -PermissionGroups AnonymousUsers -TransportRole FrontEndTransport -Usage Internet

Identity                                Bindings                                Enabled ——–                                ——–                                ——-

FRONTEND1\FromInternet                  {}                       True

  • Set receive connectors to access traffic from smart hosts if needed.
  • Set up routing of SMTP traffic to virtual DAG IP address
  • Check firewall to be sure SMTP traffic is allowed to traverse the network
  • The node to which traffic will flow is the one owning DAG IP Address (Active manager). There is info how to determine Active manager in my article:


  • SMTP traffic is not load balanced for external traffic