Well obviously Messenger stores it somewhere in memory, doesnt it? That way you wont need the protocol.
Besides, all current versions of the protocol (MSNP8, 9, 10 and the still-in-production-11) are using this header. I dont think it will *ever* go away. There is no other way for Messenger to grab the external IP for you without this (except making outside connections which is pretty .. dumb).
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