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We have 2 Exchange CAS servers running NLB. We use an outsourced SPAM provider who forwards messages to us. All of the messages from them go to a single CAS server because we only see one IP address from them.

Is there any way to configure NLB so that SMTP connections not from our network are load balanced per connection, while all other connections are balanced by source IP?

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up vote 1 down vote accepted

I think you just need to remove affinity. Affinity does a hash between ip source and destination, so you must not use that.

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I can't do that. I need affinity for our Outlook clients. – longneck Apr 24 '12 at 15:11
create 2 NLB IP, one for client and one for outside. I think you can choose affinity or not per virtual IP. – Mathieu Chateau Apr 24 '12 at 16:57
i ended up creating a second IP. the GUI for NLB implies that you can have different affinities based on port range, but any combination of rules i came up with just resulted in nothing getting through. – longneck Jun 12 '12 at 13:32

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