Will not the spammers soon learn to send their spams with
one of these addresses as bogus sender?
You overestimate the spammers :-). Most probably have no idea what IETF
is or that they're spamming an IETF list.
I dunno. I've received several complaints from people who've received
spam with my address in the From field. I don't know if I'm being
singled out by a spammer (maybe he got angry at my "I support the death
penalty for spammers" bumper sticker?), or if spammers are starting
to forge addresses in general.
But if history is any indication, spammers should not be underestimated.
They have proven quite capable of learning how to circumvent various
kinds of filtering.