But that’s the point, you can send a spoofed email to your mother that will not go into her spam folder, even if she uses Gmail.

The only way Google could protect you is if the From address is from @gmail.com (maybe, not completely sure). But if you have your own domain, you can’t have that protection. Sure, you might not be able to use Google’s own servers to send that email, but email is federated so you can use somebody else’s servers.

The only thing that stops spammers from doing more of this is the web of trust happening between email services. This is precisely why if you setup your own server, you’ll start off with a negative reputation and your emails will end up tagged as spam depending on the destination.

> But that’s the point [...]

No, that's not the point.

> Sure, you might not be able to use Google’s own servers to send that email

That is the point. Why does Fastmail allow this where Google doesn't. At best, it's ignorant and intentionally misleading. At worst, downright malicious and ripe for abuse.

There's much I don't know about email, so take what I say with a grain of salt. I imagine that maybe this could simply be a low priority issue for Fastmail because such a restriction would not be a protection for their customers but rather a restriction/disservice to them to potentially protect everyone else.

I also wonder if there are superusers that have a legitimate use for sending emails that have a different "From".

Something to think about is that, looking at the postal mail it was designed after, I don't imagine a postal office would reject me if I tried to drop off mail authored by someone else. They don't check the "From" in the envelope with my ID or anything. In fact, many envelopes don't even have a "From", and you don't even have to face a human when dropping off your mail. All the postal office does is provide access to the global delivery network for a fee.

It might be more apt to think of email providers likewise as network providers that allow transparent access to the global MTA network.

Both postal and electronic mail rely on signatures for proper authentication. It's only that electronic mail's (cryptographic) signatures are more secure but more difficult to use by laymen.

Maybe this issue ought to be thought of a similar to how illiterate people sign paper documents by making an "X". I imagine it's trivially easy to spoof documents supposedly signed by them, and even mail them. I wouldn't blame the postal office for accepting such spoofed documents.

Computers being relatively new and all, perhaps it isn't that bad to think that most of the world is still computer illiterate even if they think otherwise because of their ability to use point-and-click interfaces designed to be used even by illiterate young children.

What I think is needed is better computer education.

As to where this expectation for "From" to be validated comes from, I imagine it's something we've grown accustomed to from our use of centralized services. It would be really bad if a message on Facebook or Twitter could be spoofed, but those services are centralized, so restricting their users equates to properly protecting their users. Email, however, is decentralized. That's a good thing, and the proper way to do authentication in an decentralized service without making it more centralized can only be by non-spoofable signatures and not by trusting validations from independent service providers.

FWIW you can inbox mails from spoofed @gmail addresses on gmail.

At this point, none of the mainstream email websites or applications even show the From address, just the name that came on the email, or what matches from your address book. So, I fully expect people to get mail from [email protected] with a From name vaguely related to me and assume I sent it.