the "algorithm" in this case is very simple. Periods are stripped entirely.

[email protected] and [email protected] and [email protected] all canonicalize to the same account.

Yes, but google also prevents someone with registering an account with the same name, and ignores periods when doing that check. But your post implied that they actually had the same email address, with the periods stripped?

So, it seems likely the other person still wrote their email address down wrong - but it wasn’t the periods that they got wrong. If this is the case, then I can’t see how there is anything google could do to fix this situation.

FWIW I have <first initial><surname>@gmail.com and get loads of email intended for <first initial><their middle initial><surname>@gmail.com, apparently they just keep writing it wrong.

The service that sent that receipt was one of those 3rd party services for small vendors. You go to a bakery and they are able to magically email you a receipt, that sort of thing.

So I very much doubt the person put their email in incorrectly, but I understand your point.

The exact mechanics of how it happened I don't know, but I very much disagree with [email protected] and [email protected] resolving to the same address.