Mobile Instant Messengers (MIMs) are vastly used for communication and information sharing in recent years. However, interesting features of these applications such as group-based communication and broadcasting in channels cause rumors also to be spread in MIM networks more quickly than ordinary social networks. Although there are lots of works on modeling, analysis, and controlling rumor dissemination in social networks, the mentioned features of MIMs are not almost considered. In this paper we propose a new model for soft rumor control in MIMs that considers rumor propagation in groups and channels. By soft rumor control we mean measures for enhancing the people’s knowledge and awareness against the rumor to persuade them avoiding rumor dissemination. We suggest two soft rumor control mechanisms including a provenance based decision making process and making anti-rumor campaigns. In the first mechanism, in order to improve the ability of users to take proper actions against rumors, they are equipped with rumor provenance information including the level of trust to rumor spreader, reputation of the source of rumor and the degree of credibility of the rumor. In the second mechanism, some MIM users who have more serious concerns about the rumor effects try making an anti-rumor campaign to fight spreading the rumor. The proposed model is formalized as an extended Partially Observable Markov Decision Process (POMDP) to capture the dynamics of rumor propagation and the control mechanisms. To evaluate the proposed model, we conduct a number of extensive agent-based simulation experiments on a synthesized MIM network that show the effectiveness of the proposed mechanisms to control rumor propagation. We also conduct interesting sensitivity analysis to see the effects of different model parameters on the dynamics of the rumor propagation with control mechanisms. The proposed model helps MIM developers to provide facilities to control rumor by collective wisdom. Furthermore