Systems and methods are provided that intercept access to mainframe computing systems' messaging systems. For example, a method may include using a replacement messaging interface adapter to intercept a messaging request being directed from a client program to a messaging interface module of a messaging subsystem that is identified by a messaging stub interface module that implements a documented messaging interface. The method may also include performing an auxiliary function on the messaging request. The method may additionally include transmitting the messaging request to the messaging interface module of the messaging subsystem. The method may further include receiving a response from the messaging subsystem. Additionally, the method may include providing the response to the client program.