It is not correct. In order to need a backdoor, the service would have to be E2E in the first place, which it is not. Uninformed HNers bring this up on every Fastmail thread like it's a big deal when it has zero actual impact on Fastmail at all.
E2E isn't a requirement for something to be called a backdoor, even though governments are constantly demanding E2E backdoors.
An attacker having shell access or a government getting plaintext dumps of whatever email conversations they want (when users don't expect it) are perfect examples of backdoors. AT&T giving the NSA a secret room for them to suck up all comms, encrypted are not, is also a classic example.
