Electronic mail systems differ in the manner in which multiple recipients are handled. In some systems, the originating mail$-$handler makes all the necessary copies, and these are sent out independently. An alternative approach is to determine the route for each destination first. Then a single message is sent out on a common portion of the route, and copies are made only when the routes diverge; this process is referred to as mail bagging.

a$.$ Leaving aside considerations of security, discuss the relative advantages and disadvantages of the two methods.

b$.$ Discuss the security requirements and implications of the two methods.