This morning's news reported intentions by AOL and Yahoo! to provide certain delivery of email for the price of stamp.
We all know the current situation that email sent may not be delivered or may be delivered into a spam filter. As Ariel Rubinstein identified almost two decades ago, this presents real problems for reliable coordination. (His paper is conveniently available on-line).
The problem is simple: if you and I need to coordinate our activities and a lack of coordination is really costly, then if communication between us is even slightly unreliable, we may shy away from such activities altogether. Moreover, doing simple things such as acknowledging the receipt of email can't help (and indeed may make things worse!) if the acknowledgment cannot be reliably sent.
What this means is that AOL and Yahoo!'s solution is going to have to be perfect if it is going to provide real value.