> Would you be OK with letting a company to scan and retain a copy of every letter you sent and receive in exchange for being able to not use stamps?
Assuming there were some terms and conditions on who could access those letters, sure! In fact, if the additional benefit was they would weed out all the junk mail I get to only provide me things I'd be interested in, that's even better.
Of course, this also makes the assumption that their are still other means of communication (like phone). If the only means of communicating with me are through this service, then no.
> Do you think your correspondents would be OK with it if they knew you had such arrangement?
My correspondents? Yes. Yes I do. In fact, I believe most of them would want a service like that for themselves.
For things people wanted to send privately, they could pay to have it sent to me, like they can now.
So yes, I don't see a problem.