bbdb does not collect addresses automatically

hello, I am not sure that I can post a question about bbdb here.  but
I will try.

my environment:
Gnu Emacs 22.1.1
latest gnus

basic settings:
;;========.emacs=============================
(require 'bbdb)
(setq bbdb-north-american-phone-numbers-p nil)
(setq bbdb-user-mail-names
      (regexp-opt '("xxx <at> xxxxx"
                    "xxx <at> xxxxx")))
(setq bbdb-complete-name-allow-cycling t)
(setq bbdb-use-pop-up nil)

;;=========.gnus.el============================
(require 'bbdb)
(bbdb-initialize 'gnus 'message)
;;=====================================

that's about it.  

but it does not collect email addresses at all.  I should, am I right?

I can type "C-x bbdb-create" and create new entries independently, and
when writing mails I can enter the registered address by hitting
"Tab".