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I’d say combining these necessary data points is probably enough to identify me
The EFF has had a couple of websites that would profile you on exactly this data, so you’re completely correct in that even the basic normal required metadata is more than enough to identify you pretty well.
coveryourtracks.eff.org is where it’s living now, and a quick glance shows that just using browser capabilities and such is absolutely enough to identify me.
Universiality, basically: almost everyone, everywhere has an email account, or can find one for free. As well as every OS and every device has a giant pile of mail clients for you to chose from.
And I mean, email is a simple tech stack and well understood and reliable: I host an internal mail server for notifications and updates and shit, and it’s rapid, fast, and works perfectly.
It’s only when you suddenly need to email someone OTHER than your local shit that it turns to complete shit.