I have CUCM/Unity 10.5.2 with Demo licence and I have a SIP trunk between those 2. I create a RG/RL/RP with voicemail pilot 8000 and added to.trunk.
The problem is that when I press the voicemail key the call go to voicemail but when I want to send a message nothing happen after I register 1 message. And when I check the devices no new message received but I have the message on the CIPC ( SIP ) You Have Voice Mail, it's like the recorder not working in Unity.
So, if you look at the mailbox in Unity connection you see the #messages increase by 1 and the mailbox size increasing? Perhaps you have issue with RTP from the phone to CUC server? After you record the message can you have it re-played before sending?
Is there a firewall in front of CUC that could be blocking the RTP stream? Your best option would be to get packet capture on Unity Connection to see if the RTP packets make it there.