I have been pointed to a paper that addresses the problem of receiving messages anonymously without using a return path: David A. Cooper, Kenneth P. Birman: Preserving Privacy in a Network of Mobile Computers. IEEE symposium on Security and Privacy, May 1995. http://cs-tr.cs.cornell.edu/TR/CORNELLCS:TR95-1490 Their solution is similar to the one recently described by Matt Ghio on cypherpunks. Many of you sure are aware of the BABEL anonymous remailer developed by Ceki Gülcü and Gene Tsudik of IBM Zurich, but I have not seen it mentioned here. Their proposal for return paths is a significant improvement over cypherpunk-style reply blocks, but I still think that return addresses should be provided via message pools or similar means, while the mix net is used only to send messages anonymously. The paper, which is cited in the papers on Crowds and Onion Routing, contains a well thought-out section motivatiting the use of anonymous e-mail. Ceki Gülcü, Gene Tsudik: Mixing Email with BABEL. Proceedings of the Symposium on Network and Distributed Systems Security (SNDSS '96). http://http://www.isi.edu/~gts/paps/gt95.ps.gz