Public IM Conversation issue between Yahoo! Messenger 8.1 and earlier and Microsoft Office Communicator

Problem: 

Issue is that when a Communicator client sends a message to a Yahoo! Messenger client that is at a version less than 8.1.0421 the Communicator client does not receive notice that the message was not delivered in real time and does not see presence of the Yahoo! contact.

The Yahoo! contact receives the following message:
System: Your contact is using Windows Live™ (MSN) Messenger, and wants to add you to his or her Messenger List. To start sharing instant messages, you'll first need to get the latest Yahoo! Messenger with Voice at https://messenger.yahoo.com

The Yahoo user signs out and back in and now receives the messages from the Communicator user as offline messages and is asked if they want to add the Communicator contact to their Messenger List.  Upon doing so the Yahoo user and the Communicator user can see each other’s presence and the Yahoo user can IM the Communicator user but the Communicator users IMs do not reach the Yahoo user.

Resolution:

Encourage your contacts that use Yahoo! Messenger to upgrade their Yahoo! Messenger client.

Additional Information: https://www.ymessengerblog.com/blog/2008/11/10/changes-to-firewall-access/