Hello-

I am only working with Gnus 5.5, so I don't know if this is fixed in
Quassia, but given the discussion on xemacs-beta, it doesn't seem to be.

In `message-make-fqdn', we get the result of `message-user-mail-address'.
This can be nil, but we don't check that in `message-make-fqdn'.

Here is the patch (and ChangeLog) against 5.5.  I don't know the right
way to handle this in XEmacs 19.16, 20.3 (pre-release), or the Gnus
development cycle.  I assume that Steve and Lars can work that out.