Sure, but the law doesn't care whether you sold me something as an investment or not. It cares that you sold me something under terms that were legal in the pla

Sure, but the law doesn't care whether you sold me something as an investment or not. It cares that you sold me something under terms that were legal in the place where the transaction was made, that the contract was entered into voluntarily by adults with legal authority to make decisions, etc. What you're describing is perfectly true under the terms of service of pretty much any email provider, but that's only because the contracts governing your interaction with those providers are written in a way that makes it true. Fastmail's lifetime plan has a different contract, and under that contract, it's simply not true that you're paying to use the account temporarily. You're paying to have perpetual access to that account as long as the company exists as a legal partner to the contract they signed.