I have successfully created an account in Zimbra Desktop that mirrors my Yahoo!Mail account.

Then I started a major restructuring of my mail folders locally, from inside the Zimbra Desktop.

Here and there I had synch automatically starting up, sometimes successfully (ending with a green circle), sometimes not (ending with exclamation mark in a red circle).

When I finished I started the synch forcefully (by Send/Receive button) but after that moment I could never get a successful synch.

As a matter of fact, I cannot see any discrepancies now between the local version of folder system in Zimbra Desktop, and the remote version at the Yahoo! site. But:
1) I would like to have a reliable reporting of faults, so that the next time there is something wrong with the synch, I will know it at once. And if the software always reports of faults, it is of no help.
This is why I am giving here, as suggested, the debug report. (See below under 1)

2) Actually I have found one fault in the final synchronization, and I can make a guess about its origin. (I am giving this story below under 2). But then I corrected that fault manually and at the present moment, as I said, the contents of local folders (Zimbra Desktop) and remote folders (Yahoo!) are identical.

So, here are the details:

1) (sorry about Cyrillic interspersing the report, but I believe that the crucial information remains clear)

Сообщение отладки: HTTP request failed: 999: null
{must be sth like "Debug report"}

Исключение:
{"Exception"}
com.zimbra.common.service.ServiceException: system failure: Yahoo address book synchronization failed
ExceptionId:btpool0-5:1238420409968:26ccd1ad60055924
Code:service.FAILURE
at com.zimbra.common.service.ServiceException.FAILURE (ServiceException.java:253)
at com.zimbra.cs.mailbox.SyncExceptionHandler.checkRe coverableException(SyncExceptionHandler.java:40)
at com.zimbra.cs.offline.ab.yab.YabImport.importData( YabImport.java:68)
at com.zimbra.cs.offline.OfflineImport.importData(Off lineImport.java:88)
at com.zimbra.cs.offline.YMailImport.importData(YMail Import.java:53)
at com.zimbra.cs.datasource.DataSourceManager.importD ata(DataSourceManager.java:154)
at com.zimbra.cs.mailbox.LocalMailbox.importData(Loca lMailbox.java:417)
at com.zimbra.cs.mailbox.LocalMailbox.syncAllLocalDat aSources(LocalMailbox.java:389)
at com.zimbra.cs.mailbox.LocalMailbox.sync(LocalMailb ox.java:431)
at com.zimbra.cs.service.offline.OfflineSync.handle(O fflineSync.java:49)
at com.zimbra.soap.SoapEngine.dispatchRequest(SoapEng ine.java:429)
at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.jav a:286)
at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.jav a:160)
at com.zimbra.soap.SoapServlet.doPost(SoapServlet.jav a:269)
at javax.servlet.http.HttpServlet.service(HttpServlet .java:727)
at com.zimbra.cs.servlet.ZimbraServlet.service(Zimbra Servlet.java:190)
at javax.servlet.http.HttpServlet.service(HttpServlet .java:820)
at org.mortbay.jetty.servlet.ServletHolder.handle(Ser vletHolder.java:487)
at org.mortbay.jetty.servlet.ServletHandler.handle(Se rvletHandler.java:362)
at org.mortbay.jetty.security.SecurityHandler.handle( SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(Se ssionHandler.java:181)
at org.mortbay.jetty.handler.ContextHandler.handle(Co ntextHandler.java:716)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebA ppContext.java:406)
at org.mortbay.jetty.handler.ContextHandlerCollection .handle(ContextHandlerCollection.java:211)
at org.mortbay.jetty.handler.HandlerCollection.handle (HandlerCollection.java:114)
at org.mortbay.jetty.handler.HandlerWrapper.handle(Ha ndlerWrapper.java:139)
at org.mortbay.jetty.handler.RewriteHandler.handle(Re writeHandler.java:176)
at org.mortbay.jetty.handler.HandlerWrapper.handle(Ha ndlerWrapper.java:139)
at org.mortbay.jetty.Server.handle(Server.java:313)
at org.mortbay.jetty.HttpConnection.handleRequest(Htt pConnection.java:506)
at org.mortbay.jetty.HttpConnection$RequestHandler.co ntent(HttpConnection.java:844)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser. java:644)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpPa rser.java:211)
at org.mortbay.jetty.HttpConnection.handle(HttpConnec tion.java:381)
at org.mortbay.io.nio.SelectChannelEndPoint.run(Selec tChannelEndPoint.java:396)
at org.mortbay.thread.BoundedThreadPool$PoolThread.ru n(BoundedThreadPool.java:442)
Caused by: com.zimbra.common.service.ServiceException: system failure: Contact sync error
ExceptionId:btpool0-5:1238420409953:26ccd1ad60055924
Code:service.FAILURE
at com.zimbra.common.service.ServiceException.FAILURE (ServiceException.java:253)
at com.zimbra.cs.offline.ab.yab.SyncSession.sync(Sync Session.java:85)
at com.zimbra.cs.offline.ab.yab.YabImport.importData( YabImport.java:66)
... 33 more
Caused by: org.apache.commons.httpclient.HttpException: HTTP request failed: 999: null
at com.zimbra.cs.offline.util.yab.Request.sendRequest (Request.java:91)
at com.zimbra.cs.offline.util.yab.Request.send(Reques t.java:55)
at com.zimbra.cs.offline.util.yab.SyncRequest.send(Sy ncRequest.java:79)
at com.zimbra.cs.offline.ab.yab.SyncSession.syncData( SyncSession.java:99)
at com.zimbra.cs.offline.ab.yab.SyncSession.sync(Sync Session.java:83)
... 34 more

Если эта проблема возникает снова, опубликуйте описание и данные журнала отладки здесь.
{sth like "If the problem persists, publish the description and the log data here"}

2) The alleged origin of the problem.

Originally I had two emails with identical headings (say "ABCD") in my Inbox folder at Yahoo!, both from the same correspondent, and both with my replies. But those emails were sent at a time distance of six months, and it was important to me to distribute them over different folders, when I did the local restructuring of mail folders under Zimbra Desktop. However, initially I had the "By Conversation" View Option in Zimbra Desktop, and those emails were merged in one "conversation". I made a number of attempts to separate that conversation and distribute those emails over two different folders, but it was only when I changed the View Option to "By Message" that I succeeded.
Nevertheless, the only discrepancy that I could notice after final sync was that one of those emails completely disappeared at my remote Yahoo! account. Now I know that it is better to do a major reshuffle in Zimbra Desktop when you have your View option set to "By Message", and it is no big problem with me. But I would like to receive a green circle after my next synch, when everything has been really synhronized. (as for that lost message, on the local system I moved it to a specially created folder that does not require synchronizing; and that allows me to say that _now_ all the folders that require synchronizing are identical; if only the software could confirm that..)

Thank you in advance.