I am trapped in the following problem plz help me. Suppose a process A sends a message to process B. The process B will receive the message with MPI_Recv with MPI_ANY_SOURCE in the source argument. Let say process B does not know that A is the sender. But I want B to receive message from process A (the one who actually sends the message to process B). But if I use MPI_ANY_SOURCE, then any message from any source is captured by process B (let say there are other processes sending messages). Instead of MPI_ANY_SOURCE I cannot use A in the source argument as B does not know about the sender. What should I do in this situation ?