This notion that any third party = spam is ridiculous on its face, not to mention that new protocols can - and in this case, Apple already does - integrate anti-spam measures like PoW.
But also, it's rather ironic that you brought up email, given that this is a widely successful open protocol where random third parties connect to the server (thereby consuming resources by their email provider, the horror!) to deliver an email to the user. I'm really glad that fundamental protocols like these were developed before this kind of thinking became widespread; at least now we get to enjoy having somewhat open Internet for a little while longer.
But also, it's rather ironic that you brought up email, given that this is a widely successful open protocol where random third parties connect to the server (thereby consuming resources by their email provider, the horror!) to deliver an email to the user. I'm really glad that fundamental protocols like these were developed before this kind of thinking became widespread; at least now we get to enjoy having somewhat open Internet for a little while longer.