Chelsea Manning was imprisoned over something very different: she was a US soldier, not a private citizen, and she made public internal government documents, not a letter explicitly addressed to her.

Different standards do (and, IMO, should) apply to leakers who are government employees or members of the armed forces with a security clearance and to private citizens who are not 'leaking' something but rather sharing something they did not explicitly and voluntarily (through a contract or NDA) agree not to disclose.

And yet the non-military CJ system can be brutal and harsh. I'd imagine it's certainly possible the first person to disobey a NSL might be made an example of, especially depending on who is in charge of the executive branch at the time. You could be locked in solitary for years until you lose your mind. You could be assigned to prisons in such a way the authorities ensure you would be repeatedly beaten and raped. You could be indefinitely detained without trial or attorney -- the crime is national security related, after all. There is a horde of horribly nasty things that could be done to you even if you aren't military or security clearance. It's worse for the military, but it's bad enough for the rest of us.

Perhaps unlikely, but certainly very scary.

Also, if you disclose that you received a NSL, that probably means you at least read the thing you're leaking before leaking it.