With the screenshot attached - you are using the plug-in - so, this is still sending the message over to the ESA and presenting to the content filter you'd have in place with tagging.
You would have to have a separate inbound/outbound mail policy created that would not include the content filter you use for encryption - so that way, messages from that IP range/host would not be tagged for your encryption policy.
I hope this helps!
-Robert
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