Error on sync and strange duplication of sent mails (ERROR: command: CHECK => socket error: <class 'ssl.SSLError'>)

[Frederik]

Hello there!

I've been using offlineimap for some months now and everything was fine
until last week, when I started to experience very strange behaviour.

I synchronize multiple imap accounts but one specific folder on one
specific server troubles me: Each time I run offlineimap, recent
messages in the "Sent"-folder of that server gets duplicated. So when
running offlineimap per cronjob this populates my Sent-folder with
copies of sent messages -- note that the duplication of messages only
happens to messages newer than one week or so. Older messages don't get
duplicated.

The corresponding error goes like this:

$ offlineimap -q -o -f Sent
OfflineIMAP 6.5.4
  Licensed under the GNU GPL v2+ (v2 or any later version)
Account sync uni:
 *** Processing account uni
 Establishing connection to imap.someserver.de:143
Folder Sent [acc: uni]:
 Syncing Sent: IMAP -> Maildir
 Copy message 1552 (1 of 1) uni-remote:Sent -> uni-local
 Copy message -1 (1 of 1) uni-local:Sent -> uni-remote
 ERROR: command: CHECK => socket error: <class 'ssl.SSLError'> - [Errno
1] _ssl.c:1359: error:140943FC:SSL routines:SSL3_READ_BYTES:sslv3 alert
bad record mac
 ERROR: Syncing folder Sent [acc: uni]
  command: CHECK => socket error: <class 'ssl.SSLError'> - [Errno 1]
_ssl.c:1359: error:140943FC:SSL routines:SSL3_READ_BYTES:sslv3 alert bad
record mac
 ERROR: ERROR in syncfolder for uni folder Sent: Traceback (most recent
call last):
  File "/usr/lib/python2.7/site-packages/offlineimap/accounts.py", line
446, in syncfolder
    localfolder.syncmessagesto(remotefolder, statusfolder)
  File "/usr/lib/python2.7/site-packages/offlineimap/folder/Base.py",
line 526, in syncmessagesto
    action(dstfolder, statusfolder)
  File "/usr/lib/python2.7/site-packages/offlineimap/folder/Base.py",
line 409, in syncmessagesto_copy
    register = 0)
  File "/usr/lib/python2.7/site-packages/offlineimap/folder/Base.py",
line 335, in copymessageto
    new_uid = dstfolder.savemessage(uid, message, flags, rtime)
  File "/usr/lib/python2.7/site-packages/offlineimap/folder/IMAP.py",
line 575, in savemessage
    (typ,dat) = imapobj.check()
  File "/usr/lib/python2.7/site-packages/offlineimap/imaplib2.py", line
655, in check
    return self._simple_command('CHECK', **kw)
  File "/usr/lib/python2.7/site-packages/offlineimap/imaplib2.py", line
1595, in _simple_command
    return self._command_complete(self._command(name, *args), kw)
  File "/usr/lib/python2.7/site-packages/offlineimap/imaplib2.py", line
1360, in _command_complete
    typ, dat = rqb.get_response('command: %s => %%s' % rqb.name)
  File "/usr/lib/python2.7/site-packages/offlineimap/imaplib2.py", line
173, in get_response
    raise typ(exc_fmt % str(val))
abort: command: CHECK => socket error: <class 'ssl.SSLError'> - [Errno
1] _ssl.c:1359: error:140943FC:SSL routines:SSL3_READ_BYTES:sslv3 alert
bad record mac

---------------------------------------------------

offlineimap -q -o --info -f Sent
OfflineIMAP 6.5.4
  Licensed under the GNU GPL v2+ (v2 or any later version)
Remote repository 'uni-remote': type 'IMAP'
Host: imap.uni-konstanz.de Port: None SSL: False
Establishing connection to imap.someserver.de:143
Server supports ID extension.
Server welcome string: * OK [CAPABILITY IMAP4rev1 LITERAL+ ID ENABLE
STARTTLS AUTH=DIGEST-MD5 AUTH=CRAM-MD5 AUTH=NTLM AUTH=PLAIN AUTH=LOGIN
SASL-IR] someserver.de Cyrus IMAP v2.4.13 server ready
Server capabilities: ('IMAP4REV1', 'LITERAL+', 'ID', 'ENABLE', 'ACL',
'RIGHTS=KXTE', 'QUOTA', 'MAILBOX-REFERRALS', 'NAMESPACE', 'UIDPLUS',
'NO_ATOMIC_RENAME', 'UNSELECT', 'CHILDREN', 'MULTIAPPEND', 'BINARY',
'CATENATE', 'CONDSTORE', 'ESEARCH', 'SORT', 'SORT=MODSEQ',
'SORT=DISPLAY', 'THREAD=ORDEREDSUBJECT', 'THREAD=REFERENCES',
'ANNOTATEMORE', 'LIST-EXTENDED', 'WITHIN', 'QRESYNC', 'SCAN', 'XLIST',
'URLAUTH', 'URLAUTH=BINARY', 'X-NETSCAPE', 'LOGINDISABLED',
'COMPRESS=DEFLATE', 'IDLE')

folderfilter= lambda f: f in ['Sent']

folderincludes= []

Folderlist:
 Drafts (disabled)
 INBOX (disabled)
 Junk (disabled)
 saved-messages (disabled)
 Sent
 Trash (disabled)

Local repository 'uni-local': type 'Maildir'
Folderlist:
 INBOX
 Drafts
 saved-messages
 Junk
 Trash
 Sent

---------------------------------------------------

The rather long debug log generated via
    "offlineimap -q -o -f Sent -d imap,maildir -l debug.logfile"
is available here: http://pastebin.com/x4TQmFCB

When I first encountered this problem I deleted my local mail directory
for this server just as the data associated to this account in
~/.offlineimap. Also I deleted the duplicated messages from the server
via a web interface. After that "offlineimap -q -o" runs through nicely
without any errors. But when I then send a mail from this account and a
copy of the sent mail gets stored into the "Sent"-folder thereafter the
very same problem occurs again.

The first lines of error indicate a problem with SSL. The error does not
change if I disable SSL in .offlineimaprc (the logs above where made
with the "ssl = no" option).

Any hint is greatly appreciated!
Regards

-- 
Frederik