nnml -> nnimap (preserving Xrefs)

[Sean Doran <smd@ebone.net>]

Hi -

   I thought I did something very clever with the
following nnimap-split-rule and a small function.
I use it as follows:
        1/ enter nnml group
        2/ M P a
        3/ B m nnimap+server:~/Mail/IMAP/INBOX
        4/ leave (now-empty) nnml group
        5/ in group buffer, point on an nnimap+server: group
        6/ M-g

   It's a bit of a hack, but the net result is that
anything that was caught by my previous nnmail-split-fancy
is now cross-posted into multiple nnimap groups, with
marks preserved.  I'm pretty happy.  However, now I have
two problems.

   First problem: it took a bit to realize I needed the
                  "my-imap-splitter" function to avoid
                  EVERYTHING being crossposted into "misc"
                  (instead of just new mail being moved there)
                  I (naively) did "mv misc INBOX" + M-g
                  and now there are *lots* of duplicates
                  in each group.   How do I get rid of them?

   Second problem: How does anything know that the
                   the nnimap-split-rule crossposted an
                   article?  That is, how do I get marks
                   to propagate to all the groups an
                   nnimap article is crossposted into?

   Any help in migrating a huge pile of large-ish, heavily
crossposted nnml groups into nnimap will be appreciated!

        Sean.

(setq nnimap-split-rule 
      '(("server"
	 (".*"
	  (("~/Mail/IMAP/\\5" "^Xref: .+ \\(.+\\):.+ \\(.+\\):.+ \\(.+\\):.+ \\(.+\\):.+ \\(.+\\):.+")
	   ("~/Mail/IMAP/\\4" "^Xref: .+ \\(.+\\):.+ \\(.+\\):.+ \\(.+\\):.+ \\(.+\\):.+")
	   ("~/Mail/IMAP/\\3" "^Xref: .+ \\(.+\\):.+ \\(.+\\):.+ \\(.+\\):.+")
	   ("~/Mail/IMAP/\\2" "^Xref: .+ \\(.+\\):.+ \\(.+\\):.+")
	   ("~/Mail/IMAP/\\1" "^Xref: .+ \\(.+\\):.+")
	   ("~/Mail/IMAP/misc" my-imap-splitter))))))

; we have to allow crossposting here...
(setq nnimap-split-crosspost t)

(defun my-imap-splitter (group)
  "called with the headers narrowed, returns t iff there is no ^Xref: line, nil otherwise"
  (let ((regexp "^Xref: "))
    (goto-char (point-min))
    (progn (not (re-search-forward regexp nil t)))))