In a method of controlling a network of interconnected publish/subscribe message brokers for routing publications from a plurality of publishers to interested subscribers, each message broker is arranged to receive publications from publishers both directly and via other brokers and to receive subscriptions and unsubscriptions from subscribers and other brokers for publications meeting predefined criteria identified in the subscriptions or unsubscriptions. Each broker creates and manages a list correlating subscribers with the predefined criteria. It then matches received publications with the subscription list and forwards publications which match listed subscriptions which are in an active state to interested subscribers and interested other brokers in the list. Also, in response to received subscriptions and unsubscriptions, each broker generates and forwards proxy subscriptions and proxy unsubscriptions to other brokers. Each broker establishes a retention period for subscriptions. Then, in response to receipt of an unsubscription from a subscriber or a proxy unsubscription from another broker, it retains the corresponding subscription in a retained state for the retention period. During the retention period, matching publications will not be forwarded to the subscriber or other broker and no proxy unsubscriptions will be forwarded to other brokers. A new subscription for the same matching publications as the retained subscription during the retention period causes a reversion of the retained subscription to its active state. Propagation of proxy subscriptions and unsubscriptions is thus reduced in dependence on the duration of the retention period.