On-prem I have 2 Exchange 2016 servers that are load balanced with ARR 3.0

Now I'm going to configure hybrid on both servers.

They need to be directly accessible by Exchange Online on port 25 to enable hybrid mail flow.

Since I want this connection to go to both Exchange servers and since I also want it to be high available, how can I do this?

ARR 3.0 does not support SMTP load balancing if I am correct, right?

Do I need a second public IP for this?

Thanks a lot for the help already!

  • For now I only see these options: 1) Extra public IP with a public DNS A record for each of the public IPs so there is DNS Round Robin for SMTP traffic 2) Forward all SMTP traffic to the DAG IP address. In this case there is active/passive failover. However, I can't find any information about this "non-standard" setup. I know a DAG IP is not meant to be used for this but it does seem to work for SMTP traffic. 3) Get a hardware load balancer to load balance SMTP traffic (costly and not an immediate option unfortunately). – Jozef Woo Aug 8 '17 at 11:16
  • If it is just for SMTP traffic, then the free load balancer from Kemp would work, as SMTP traffic isn't that great. Otherwise another IP address is your only option - and the one I would prefer to use. SMTP isn't really designed to be load balanced. – Sembee Aug 8 '17 at 12:19
  • Hi Sembee, thanks for that valuable input! I was thinking to use the DAG IP for it. What do you think? – Jozef Woo Aug 9 '17 at 19:09
  • Not a supported configuration. Not something I have ever done, or would even consider doing. – Sembee Aug 10 '17 at 9:50
  • Hi Sembee, thanks. I would choose your answer as the best answer but I can't because it's a comment. – Jozef Woo Aug 11 '17 at 10:31

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