E-mail lists are generally closed. That means that only subscribers can post or read messages. The chances of being spammed are much lower than on the Usenet. Rather like an email version of a newsgroup or bulletin board, and the same rules apply for the most part.
For even more book-related lists, try Email
Lists for Booklovers.
Tolkienlist: On this mailing list, you can discuss all things Tolkien to your heart's content.
The Bibliophile Mailing List (aka Biblio): An email list which you subscribe to. You will receive email messages from other members of the list, and be able to post your own messages. This is a very busy list. It has something over 1000 subscribers, and some days it seems like most of them have something to say... Many of the members are booksellers, and posting a want here is pretty likely to get some kind of response.
UK Books: Good for finding books published in Britain, as many members are based in the UK and Europe.
Antiqbook: European rare and antique books.