Here's something that ought to be on the manpage.
Import your current inbox into its address list with something like this:formail -X From: -X To: -X CC: -s lbdb-fetchaddr < /var/spool/mail/myusername
Then you hook it into your procmail so it gets all new addresses (that is in the manpage), and you can then point it at other sources for data.
Now, when I query "lee" from mutt, it finds (among others, emails screened for privacy):
|1||Eileen Hash||esp@||2004-02-09 13:01|
|2||kathleen patricia brennan||kpb@||alias Kathleen|
|3||Lee Colleton (Q: Reality?)||lee@||(GnuPG)|
Which shows it's pulling email address from my incoming mail, my mutt aliases, and my GPG keyring. Fancy.