In previous Sametime 9.0.x limited use version, Offline Message function cannot be used for limited license.
For Sametime 11.x ( not premium), Customer can use it free with Notes/Domino license, so it's almost the same as former limited Use version. But offline messaging is enabled by default. And because Sametime 11.x provided persistent chat which can also sending chat message to offline user, it is no need to use former offline messaging function.
Furthermore there is a Jira Ticket SAME-44569 which indicate Offline Messaging Function does not work properly on Sametime 11.x.
For the above reason Offline Messaging on Sametime 11.x only make customer confusing, no real value.
I suggest we can remove or disable Offline Messaging function by default in future version HCL Sametime product.