That can't be avoided short of having a mail service with plentiful full aliases on a shared domain. They could just use the heuristic that unless you're at one of the well known email providers like Gmail, your domain name might be personal and therefore count as part of your global identity, without even considering what comes before the @.

So it doesn't really matter much whether I go with [email protected], or [email protected].

To deal with that for good you'd need a pretty large set of domain names to use for this purpose.

There are already a growing number of services that won't even allow you to sign up unless you have an email at one of the large services. I never noticed until I started using my personal domain to separate work/personal after changing jobs recently.

What are some examples?

I’ve been using my own domain since the late 90s, and I’ve never run into this.

When I tried signing up for the SNL app a few years ago with snlnbc@[mydomain.com], and then [randomnickname]@[mydomain.com], it failed, but then worked with a GMail address.

Which is all kinds of ironic, because I'm old enough to remember when free emails like hotmail.com and gmail.com were rejected by a lot of sites!

From personal experience, "new" Flickr makes it difficult to signup when you use a personal domain versus one of the top 10 known email providers.

> If you do something obvious like use [email protected] at amazon, you should expect them to add a rule that [email protected] gets cleaned up to "@example.com"

It seems like a very error prone thing to do automatically, while reaping little in return for the effort. How much do advertisers stand to gain by adding special case heuristics for "people who might be using an unshared email domain with a per-site local-part?"

If I give my email as [email protected], normalizing it to [email protected] is just applying a bit of common knowledge about how an email service with billion(s?) of users handles the + sign in the local-part of an address. It's a carve out, but it's totally deterministic (for Gmail at least) and applies to a lot of users.

If I give my email as [email protected], normalizing it to @2d0d4809.com involves guesswork about that specific domain. I don't think normalizing away the + sign in the first case implies we should expect the latter to get normalized into a single identity as well.

I really don't know anything about the ad space but the linked project seems to indicate that ids get grouped into value classes. It describes IDs built off of normalized emails and also off of phone numbers to create identity-validated IDs which are of higher value in the ad market. Obviously phone numbers will be the most useful of the validated IDs and emails normalized.

Of course if you have "@gmail.com" that's not going to have any value vs the identity-validated alternative. But at the bargain bin end of the ad selling universe does "[email protected]" that has never been seen anywhere except amazon have more value than "@2d0d4809.com" that has been seen recently in a handful of other places consistent with use by a single person? It's obviously not an identity-validated ID class, so it's not going to demand identity-validated bids. But having a tracking history might add a tiny bit to the bid. So I wouldn't put it past people to use that rule.

I don't even think the Heuristics would need to be that complex. Big email still uses reputation lists to determine if they should junk an email, so applying sender reputation, or lack thereof, to the domain part could be good enough to safely hash as an identity.