1 * configurable constants (quote folding, index limits)
2 * use tags as date-based skiplists for navigating history
3 * per-message views should be able to quickly navigate to replies.
4 (n.b.: this is SMTP, we must account for out-of-order delivery)
5 * search, Xapian bindings are pretty common on GNU/Linux distros
6 * NNTP server (is there demand for one?)