The only way I see to stem the flow is to incur a cost to sending traffic.
In the case of email it may be too late, and maybe for RSS also by now however yound it is.
Some sort of mechanism would have to be found by which the sender pays the receiver for each sent item. When the receiver is also a sender himself it could be set up so that the ballance is automatically calculated in order to prevent a huge number of microtransactions (this seems the most likely thing that could possibly work for email if enough ISPs cooperate).
Non-paid feeds would still be available, but use at your own risk.
If the sender pays that does several things:
1) it makes him more likely to vigorously check his systems for exploits that spammers could use to spam through him
2) it makes him think twice about spamming himself
3) it makes him think twice about posting trivialities.

All would reduce the amount of garbage sent.