[benjoffe]

Personally I would hate to receive email like this, if I viewed the email on my phone I won't be able to view it on my work computer. If I'm working from home the next day I won't be able to view the message (ever again!). If I want to view the email in several months time I'm assuming it's highly unlikely I'll be able to.

Maybe there's a market for this, and if so good for you, but my honest feeling is that any desire for such a 'protection' is better solved by either talking to the person on the phone or in person, or getting them to sign an NDA, or if the recipient is so untrustworthy then don't engage with them.

[fec]

Temporary solution: If you have multiple devices, you can create an account on NOFWD, and log into nofwd.com from each device. Now, NOFWD will see all of your devices as a single entity, and not self-destruct your messages that you view. This behavior can be ended by logging out again.

Long term: More generally, I want to expand the fingerprinting and management technology, so that the system can automatically learn users and not flag false-positives. Imagine how Paypal or Facebook detects that you're not logging in from one of your usual locations.

NDAs and other legal contracts are one existing solution to this problem, but those are very slow and heavy-weight. This is meant to be very fast and light-weight. Neither solution is bulletproof. Instead of choosing though, you could use both!

[benjoffe]

The problem with your multiple device solution is that it puts burden on the recipient, who's highly likely to have any idea what NOFWD is. The fingerprinting solution you outline next is highly flakey as well, as it would require a critical mass of users to gather the necessary data, and even then the kind of algorithms you'd need are orders of magnitude more complex than the ones Facebook etc. use, as those catch instances of users logging in from foreign countries (or perhaps states), and would not catch cases where the 3rd party is in the same city, a very likely case.

A typical scenario I imagine is that the recipient will lose the message, and end up emailing or calling back for the same information, which will annoy all parties (or possibly worse, they'll lose the information and ignore it forever), as well as require the information be transmitted more times than usual (something someone security conscious probably won't like).

I hate to be so critical of this service, but I just can't see this being useful. I wouldn't call this hitting a nail with a sledgehammer, it's more like hitting a nail with a six foot ceramic feather.