As I am given to understand it, as of 7.0 network address translation involving ipfw no longer involves natd(8). If true, then the chapter (29.9 in the online version, 27.8 on disk) is outdated.
For bugs matching the following criteria: Status: In Progress Changed: (is less than) 2014-06-01 Reset to default assignee and clear in-progress tags. Mail being skipped
(In reply to roberthuff from comment #0) Chapter 29 online is now: > Electronic Mail <https://docs.freebsd.org/en/books/handbook/mail/>
(In reply to Graham Perrin from comment #2) https://docs.freebsd.org/en/books/handbook/firewalls/ (now chapter 31)