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Need help unmasking internal VIP address for on premise Exchange

Dave Ratliff

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I've recently inherited an on premise Exchange 2013 environment (hybrid with Exchange Online) that we use for relaying SMTP. It only consists of two servers with the NetScaler configured to RoundRobin port 25 and LeastConnection for ports 110 and 443. My issue pertains to port 25 traffic.


It's come to my attention that port 25 traffic relays without issue so long as it's to Exchange Online recipients in our domain, but if to outside our organization fails to relay. If I add the NetScaler's VIP to our restricted receive connector, emails relay outbound properly but inbound SMTP from Exchange queues Pending due to the inability for the Exchange Online connector to traverse the receive connector. After kicking this around and using DNS round Robin as a workaround, Microsoft claims that I simply need to "unmask" the internal facing VIP address. 


Case in point, our LB VIP is internally IP'd as but if I putty to it on port 25, Exchange sees me as (this is the IP that when added to the receive connector breaks Exchange Online traffic). It is possible to do away with the IP and have my connection show my actual IP that I'm truly connecting from?  I see that the IP is configured Subnet IP address but not clear the ramifications if we were to remove it. 


For what it's worth, ours is a NetScaler 8200 (I believe) on version NS10.5: Build 56.22.nc, Date: Jul 9 2015. 


Pardon my ignorance but my primary responsibility is Exchange, not NetScaler management; my network team is currently behind on some higher priority projects and I thought I'd do what I could to the research. 





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