It's very old-school, but enough infrastructure survives to be usable. Remailers comprise a high-latency onion routing network for messages. By default, messages are anonymous and one-way. But reply blocks can be added, which direct replies to alt.anonymous.messages (aka a.a.m). Replies are encrypted to your public gpg key (in addition to whatever end-to-end encryption that you and your correspondent use) and are tagged with a one-way hash of your secret "this is my message" phrase. Also, new versions of Quicksilver Lite and Quicksilver AAM are fairly easy to set up and use. QSL send messages, and QSA gets all messages from a.a.m, and determines which of them are yours. They're both Windows programs, but they work well in Wine on Linux. Also, the Quicksilver folks have .onion entries to their nymserver and news server, so you can do the whole thing via Tor. Finally, QSL and QSA work well in Whonix with Wine. Is anyone interested in more on how to do this?