Analogizing to phone calls is a bad way to understand the 4th amendment because it's basically the product of a 1960's liberal court. It's a high watermark. It's law, but shouldn't be the only source you use to understand the meaning of the 4th amendment.[1]
The distinction between your papers and other peoples' papers about you is not an "artificial distinction." Where I think you're going astray is the use of the word "public." The 4th amendment doesn't protect all information that you wouldn't want made public. It's narrower than that. Say you visit a prostitute. She keeps a log of the date and length of each visit. That's obviously not "public" information. But it's also not one of your "papers" or "effects" because you neither generated that information nor are you in custody of it. It pertains to you, but you don't get to invoke privacy privileges over all information that pertains to you.
The same is true of bank records, credit card records, etc. When you entrust other people with your information, you can't invoke the 4th amendment to keep them from disclosing it, either voluntarily or pursuant to a subpoena.
[1] Also note that in the 1960's phones were analog devices with no storage capability. When you talk about things like e-mail, which go through intermediate servers and can be stored or copied by anybody in the chain, your reasonable expectation of privacy in that information is very different than what it might be for a 1960's style phone.
I think with email expectation of privacy is exactly the same. And 4th amendment, saying "papers", obviously does not mean "only something that is never recorded can be private and protected from government". Obviously papers are very permanent things.
In the same vein, then, mail should not be protected, since you give it to the postman to send, so nothing prevents them from opening the envelope, reading everything inside, copy it and tell the police. I don't see how this is any different from taking emails from private email mailbox. In both cases I expect only machines and people that need to read it for purposes of the transmission to access it, and only in parts that are necessary for such transmission to happen, and do not expect them to disclose it to anybody else.
It's not the fact that e-mail is recorded. It's the fact that e-mail is recorded and retained by third parties.
The mail example is interesting. A letter sent via FedEx or UPS is not protected by the 4th amendment. Letters sent via the Post Office are protected, because in that case the "third party" is actually an organ of the government.
By the same logic, if you rent a storage locker, it can be searched without a warrant since it belongs to a third party. Or your rental house can be searched, since you only rent it from the third party. And if you put your bag in a taxi trunk, you just gave it to a third party, so if the police stops the cab, they can search the bag without any probably cause. How does it make sense?
I don't see the logic. If you give it to the government, you can expect privacy from the government, but if you give it to somebody else, government can take it? Makes no sense. It's like saying if you confess to the police officer, he can not testify against you, but your own lawyer has to. Completely opposite of what reasonable person would expect.
The distinction between your papers and other peoples' papers about you is not an "artificial distinction." Where I think you're going astray is the use of the word "public." The 4th amendment doesn't protect all information that you wouldn't want made public. It's narrower than that. Say you visit a prostitute. She keeps a log of the date and length of each visit. That's obviously not "public" information. But it's also not one of your "papers" or "effects" because you neither generated that information nor are you in custody of it. It pertains to you, but you don't get to invoke privacy privileges over all information that pertains to you.
The same is true of bank records, credit card records, etc. When you entrust other people with your information, you can't invoke the 4th amendment to keep them from disclosing it, either voluntarily or pursuant to a subpoena.
[1] Also note that in the 1960's phones were analog devices with no storage capability. When you talk about things like e-mail, which go through intermediate servers and can be stored or copied by anybody in the chain, your reasonable expectation of privacy in that information is very different than what it might be for a 1960's style phone.