It's part of the reason why you see many places ask for your phone number, not that I agree with that, and even this method has many flaws.
Instead, all anyone offers in this vein are identifiers that are really annoying to get and that nobody already has as a matter-of-course of registering a company; such that many real companies can't (or won't bother to) pass them. DUNS numbers are a common choice. Our company is five years old and doesn't have a DUNS number. It takes two weeks to get one. So how could I expect our customers to bother getting one just to try our product?
Of course in principle you can get an EV cert for any company as well, but now we're talking about determining whether a company is sufficiently well-known to accept, which is not something that can fully be solved deterministically since that's a human judgement, there will always be some grey areas. But, there are certainly a lot of companies that could probably be "automatically verified" in some fashion (ford motor company? reasonably well-known, and this is their domain...) given some sort of authoritative domain -> stock mapping, and that's not impossible to do if you trust the EV scheme.
Anyway, not perfect, but challenges based raises the bar a lot from "register domain with godaddy and sign up for let's encrypt" to "first you have to get an EV certificate..."
Of course, since such a mechanism is not widely used... not exactly going to find tons of official support for using it like that. But the mechanisms are there!
Also, as a slight tweak, I'd hope that this authentication scheme would only admit legal companies that are at least a week old. People who do these sorts of bulk-registration attacks tend not to be patient people, willing to wait around for their credentials to gain reputation before using them. They create them and then try to use them right away. Whereas no real company would be signing up for most B2B services in its first week of legal existence. (Google Workspace? Sure. Accounting software? Probably not.)
If it's targeted to X company for a specific reason, they'll wait however long they need. If it's generic and X company is just caught in the crossfire, then maybe.
>Whereas no real company would be signing up for most B2B services in its first week of legal existence. (Google Workspace? Sure. Accounting software? Probably not.)
When I've registered companies in the past, it's when I have sales. Before then, it's just an idea to see if we get users. But the company with the service can determine that.
(You don't have to be petty about it; no need to send them to a "you're an attacker" page or anything. Just redline the form-field, explain the problem clearly, and let them modify the address until it's less duplicable.)
Yes, this doesn't stop people from manually registering multiple times, since, as you say, people can have multiple addresses; or even email service from multiple providers. But it does stop low-effort automated bulk-registration attacks. And some services — those with any sort of free-tier especially — get a lot of those!
It's a 100% valid character to use. Doesn't have to mean it's a label in another hostname. Goes back to what others have said. You either end up with a ton of rules, or go with the fact that email isn't the best solution to identify unique users.
https://en.wikipedia.org/wiki/Email_address#Local-part
> The local-part of the email address may be unquoted or may be enclosed in quotation marks.
>If unquoted, it may use any of these ASCII characters:
> - uppercase and lowercase Latin letters A to Z and a to z
> - digits 0 to 9
> - printable characters !#$%&'*+-/=?^_`{|}~
> - dot ., provided that it is not the first or last character and provided also that it does not appear consecutively (e.g., John..Doe@example.com is not allowed).[5]
> If quoted, it may contain Space, Horizontal Tab (HT), any ASCII graphic except Backslash and Quote and a quoted-pair consisting of a Backslash followed by HT, Space or any ASCII graphic; it may also be split between lines anywhere that HT or Space appears. In contrast to unquoted local-parts, the addresses ".John.Doe"@example.com, "John.Doe."@example.com and "John..Doe"@example.com are allowed.
(it keeps going on the wikipedia page)
(It's a similar "you're really relying on perfect competence from the whole rest of the ecosystem to get you out of this" feeling as e.g. putting a space in your user name — and thus your home directory path — in Linux. Sure, the core GNU/BSD/etc tooling has been tested for that use-case — but are you really going to trust random tools and shell-scripts to handle argument tokenization perfectly? Or are you just going to ditch the space to be safe?)
It would probably be the other way.
The more technical literate a user is, the more they'll understand and figure out how things work, the nuances, and use those things.
You know that core tooling that works? It's because technical literate users, tried it, found the issue, and fixed it.
Same way with me using é on my name. If something breaks on a website, email, etc, I create an issue and starts emailing. My name doesn't have an e, it has an é.