MMP and Webmail Server

You can put the MMP and Webmail Server on the same set of servers. The advantage to doing so is if a small number of either MMPs or Webmail Servers is required, the amount of extra hardware for redundancy is minimized. The only possible downside to co-locating the MMP and Webmail Server on the same set of servers is that a denial of service attack on one protocol can impact the others.