Question: What means:

Support for several bindings (e.g., raw HTTP, TCP, MSMQ, and named pipes)
allows to choose the most appropriate PLUMBING to transport message data.

Answer: 
'Plumbing' is a pipe system (like the one for water in your house).

It's often used in IT to mean a support infrastructure. It's a particularly suitable term in this case, since the support infrastructure is actually a transport infrastructure, kinda like pipes indeed.
In this context, plumbing refers the communication layer. If you think of your data/information as "water" then "plumbing" refers to the way the data/information moves from various parts of your system.