what pattern is used to design objects that send/receive objects?

I would love to design 2 objects of the same class that are able to send and receive a smaller object.

Let say A and B of class Person. A sends B a object of class Letter and B, after spending time reading the Letter, sends back a Reply.

I greatly appreciate if you can answer + a small example (preferably in C++ as I know only that). Thank you so much!