11. The method according to claim 1 , further comprising: responsive to determining, by the message broker, that the message is to be a retained message, retaining the message subsequent to sending the message from the message broker to each of the at least one identified subscriber; responsive to detecting, by the message broker, a new message subscriber that registers a subscription for which the registered topic matches the topic associated with the retained message and for which the registered subscriber classification information matches the classification criteria associated with the retained message, subsequently sending the retained message to the new subscriber; and reflecting the subsequent sending of the message in the comparing and the controlled failure handling.
11. The method according to claim 1 , further comprising: responsive to determining, by the message broker, that the message is to be a retained message, retaining the message subsequent to sending the message from the message broker to each of the at least one identified subscriber; responsive to detecting, by the message broker, a new message subscriber that registers a subscription for which the registered topic matches the topic associated with the retained message and for which the registered subscriber classification information matches the classification criteria associated with the retained message, subsequently sending the retained message to the new subscriber; and reflecting the subsequent sending of the message in the comparing and the controlled failure handling. 12. The method according to claim 11 , wherein the comparing and the controlled failure handling are delayed, following the sending of the message from the message broker to each of the at least one identified subscriber, to await the subsequent sending of the retained message to the new subscriber.