1. Errata

   -    In section 4.6.4, replace ".." with ".".

   -    In section 4.2.4, replace three references to 4.3.1 by
        4.2.1, and one reference to 4.2.2 by 4.1.2.

   -    In section 5.2, replace "1  mailbox" with "1#mailbox",
        "1 msg-id" with "1#msg-id" and "1 encoded-type" with
        "1#encoded-type".