A wireless communications system may include a plurality of wireless communications networks and a plurality of mobile wireless communications devices for sending and receiving wireless electronic mail (email) messages over the wireless communications networks. The system may further include a resource deployment server for storing a plurality of resource deployment packages (RDPs), where each RDP includes deployment content and deployment instructions therefor relating to sending and receiving email messages. The resource deployment server may also be for dynamically deploying RDPs to the wireless communications networks to update deployment content thereof based upon the respective deployment instructions.