Re: FAQ 5.2 still correct? [solved]

Solved!

As I said, gnus per se did not add the message-id.
I confirmed this again by using
(setq message-generate-headers-first t).
No Message-Id was generated, but mail in ~/Mail/queued-mail/
had a Message-Id.
So I had a look at smtpmail.el. This file contains these lines:

	    ;; Insert a `Message-Id:' field if there isn't one yet.
	    (goto-char (point-min))
	    (unless (re-search-forward "^Message-Id:" delimline t)
	      (insert "Message-Id: " (message-make-message-id) "\n"))

I just
- copied the file to smtpmail-changed.el
- added ;; in front of each of those three lines
- changed the last line to (provide 'smtpmail-changed)
- changed my .gnus to (require 'smtpmail-changed)

Now, my Message-Id is set by the google smtp-server ;)

Great!
Thanks to the author of smtpmail.el for extensively documenting
each single step in there!