If I understand your description of issue, it sounds as if you have a one-way audio issue. If outside callers are being redirected to Unity Connection (you could see this in the port monitor using RTMT) but do not hear the recorded greeting playing then that suggests that a firewall and/or ACL is blocking RTP from the gateway to (and/or from) Unity Connection. The media transmission once the call is redirected to Unity Connection would be gateway to/from Unity Connection.
You may need to provide more detail if this is not the case.
Hailey
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