That's a good idea, but it'll take up a lot of disk space at the machine running the remailer. Right now, remailers that provide latency don't keep an e-mail for more than about 12 hours. Once you start keeping them around for a few days (a reasonable grace period for a first-time user), it's a lot more disk space.
How 'bout this:
There is (as we all know) a newsgroup for anonymous messages, Simply encrypt the message with one half of a public key pair, and send the other to the individual with a message saying that there is a message waiting for you on alt.anonymous.messages with a subject of ^CHojnafy&Ys9. This is the key to decrypt the first level. If you do not have access to usenet, you can get the message from www.dejanews.com &etc.
I don't like this for only one reason: you'll be wasting disk space at thousands of usenet sites. I happen to think that alt.anonymous. messages is a really wasteful communications channel. If it were used for all the traffic now caried by the remailers, many syadmins would stop carrying it (a lot of useless traffic). I would have if I had carried it. :-) Also it's not fair to assume that everyone with access to e-mail can also get web or usenet. One example that's still fairly common in a user on a corporate computer behind a firewall.
The encryption by the endpoint remailer is not intended to supply complete privacy, but rather to provide an additional level of protection for those who don't encrypt to begin with.
If the key is generated by the remailer, then a LEA might go on a fishing expedition trying to figure how the key was generated and whether they can generate the same key again. It's safer not to generate random keys.
This has the benefit of (1) not dumping the email into a persons mail box, so they don't get "spam" they don't want. (2) getting possibly illegal material off the remailer machine as quickly as possible (well, off the remailer portion anyway, if the news spool is on the same machine, that is a different legal battle) and (3) disassocating the sender and receiver a little more.
These are all good things; I just wish they could be accomplished in a less wasteful manner. To replicate a file at thousands of usenet servers which can only be decrypted by one person is, in my opinion, selfish net-abuse. --- Dr.Dimitri Vulis KOTM Brighton Beach Boardwalk BBS, Forest Hills, N.Y.: +1-718-261-2013, 14.4Kbps