System and method for processing encoded messages for exchange with a mobile data communication device

A system and method are provided for pre-processing encrypted and/or signed messages at a host system before the message is transmitted to a wireless mobile communication device. The message is received at the host system from a message sender. There is a determination as to whether any of the message receivers has a corresponding wireless mobile communication device. For each message receiver that has a corresponding wireless mobile communication device, the message is processed so as to modify the message with respect to one or more encryption and/or authentication aspects. The processed message is transmitted to a wireless mobile communication device that corresponds to the first message receiver. The system and method may include post-processing messages sent from a wireless mobile communications device to a host system. Authentication and/or encryption message processing is performed upon the message. The processed message may then be sent through the host system to one or more receivers.