This paper describes a multi-agent system, called MASMA, that manages the meeting schedule of a set of users. Masma is a mixed-initiative decision support system based on agent technologies that addresses various aspects of the agenda management problem: in particular it is the result of an investigation on several issues concerning the acceptability of the agent approach by human users. The paper is focused on how the initiative moves between the different actors involved in the system: human users, personal interface agents and service agents. Two classes of control mechanisms are introduced and explained that coordinate continuous interaction among the actors. The first group concerns negotiation protocols and personalization of agents that are used as standard tools to model strategies of communication. In the second class inspection windows and heuristics are applied to avoid continuous question-answering in order to increase the acceptability of the whole system.