nnimap dies when APPENDing large messages

["Dag-Erling Smørgrav" <des@des.no>]

Client: Gnus 5.13, Emacs 23.0.95.1, FreeBSD 9 on amd64.
Server: Cyrus IMAP 2.3.16, same OS on a different machine.

I run my own IMAP server and have set up Gnus to save sent messages in
an IMAP folder using nnimap:

(setq gnus-secondary-select-methods
      '((nnimap "imap.des.no")))
(setq gnus-outgoing-message-group "nnimap+imap.des.no:INBOX.sent")

If the message, including headers, exceeds 33305 bytes, the APPEND
fails.  I get the following message:

imap-send-command: writing to process: bad address, imap

After that, as soon as I try to do anything that involves nnimap, Gnus
simply hangs.  The only workaround I've found is to restart the IMAP
server, which forces nnimap to restart the client process.

I have obtained IMAP traces of successful and failed APPENDs:

http://www.des.no/imap-ok.txt
http://www.des.no/imap-fail.txt

To summarize:

successful:

        <1277209057<2111 APPEND "INBOX.sent" {33305}
        >1277209057>+ go ahead
        <1277209057<From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no>
        To: dag.erling@gmail.com
        Subject: test
        X-Draft-From: ("nnimap+imap.des.no:INBOX.sent")
        Date: Tue, 22 Jun 2010 14:17:35 +0200
        Message-ID: <867hlr45y8.fsf@ds4.des.no>
        User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.95 (berkeley-unix)
        MIME-Version: 1.0
        Content-Type: text/plain; charset=us-ascii

        xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
        [...]
        yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy
        <1277209057<�<1277209057<yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy
        >1277209057>2111 OK [APPENDUID 1118837504 16410] Completed

The � between the left angle brackets on the second-to-last line is a
0xEC.  I have no idea what it means; I thought IMAP was a 7-bit-clean
protocol?

failed:

        <1277209098<2125 APPEND "INBOX.sent" {33306}
        >1277209098>+ go ahead
        <1277209098<From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no>
        To: dag.erling@gmail.com
        Subject: test
        X-Draft-From: ("nnimap+imap.des.no:INBOX.sent")
        Date: Tue, 22 Jun 2010 14:18:17 +0200
        Message-ID: <8639wf45x2.fsf@ds4.des.no>
        User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.95 (berkeley-unix)
        MIME-Version: 1.0
        Content-Type: text/plain; charset=us-ascii

        xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
        [...]
        yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy<1277209106<2126 NOOP
        >1277209106>2125 BAD junk after literal

DES
-- 
Dag-Erling Smørgrav - des@des.no