SSN-xx-HERE@citizen.gov is a how, which may or may not be a good one. For one, here in France, the SSN isn't as important as it seems to be in the US, so its being public is probably less of an issue. This approach would still be bad for spam or whatever.

Another how could be by using the same kind of naming in use elsewhere, as in name.surname.213@citizen.gov. Except that not anyone would be able to randomly open an account. You'd have to go through some kind of agency that would check your ID. This would allow them to expose a way of changing (in case its overrun by spam) or unlocking (in case of lost password) your account safely.

We have a more or less similar thing in France with bank accounts: you have an "opposable right" (as in, undeniable) to have a basic bank account. Not sure if this is a French law or an EU directive, but I think the same could work for email.