We are having an issue which seems to have stumpped even Cisco.
We are running CUP 8.5.2 on the server.
A MAC 7.1 user IM's a PC user using CUPC 8.5 and they receive the message fine. A reply is sent from the PC user and the MAC 7.1 client never receives it. This is happening on all of our MAC's not just one account. If this same person logs on to a PC version they can communicate without an issue. No firewall or anti-virus software exists on any of the machines.
Presence status updates without issue between the two versions the only thing that seems to not work is IM's sent from the PC version to the MAC version.
This should be a supported scenario. I have just tested it in Cisco's production network and it worked as expected. Did you contact Cisco TAC? They should be able to help you to resolve any potential issues in your environment. Thank you.