NB syncs fine with 3 yahoo accounts, just one does not.
NB but does manage to get incoming messages, and send outgoing ones ! Not sure what it is failing at (some folders in Zimbra do not have their content of emails, some deletions in Zimbra do not get synched back to ymail).

********************************

Last Sync: Unknown
Status: error
Mailbox size: 826.7 MB


Failure communicating with remote server. Please try again later.

Debug message: Unexpected tag in response(expected C08 but got C07)

Exception:

com.zimbra.common.service.ServiceException: system failure: Folder sync failed
ExceptionId:sync-mbox-davidbz@ymail.com:1366208655221:df940fee6cc603ae
Code:service.FAILURE
at com.zimbra.common.service.ServiceException.FAILURE (ServiceException.java:253)
at com.zimbra.cs.datasource.imap.ImapSync.importData( ImapSync.java:169)
at com.zimbra.cs.datasource.imap.ImapSync.importData( ImapSync.java:136)
at com.zimbra.cs.offline.OfflineImport.importData(Off lineImport.java:100)
at com.zimbra.cs.offline.YMailImport.importData(YMail Import.java:54)
at com.zimbra.cs.datasource.DataSourceManager.importD ata(DataSourceManager.java:317)
at com.zimbra.cs.datasource.DataSourceManager.importD ata(DataSourceManager.java:277)
at com.zimbra.cs.mailbox.DataSourceMailbox.syncAllLoc alDataSources(DataSourceMailbox.java:439)
at com.zimbra.cs.mailbox.DataSourceMailbox.sync(DataS ourceMailbox.java:478)
at com.zimbra.cs.mailbox.DataSourceMailbox.syncOnTime r(DataSourceMailbox.java:406)
at com.zimbra.cs.mailbox.SyncMailbox$1.run(SyncMailbo x.java:279)
at java.util.TimerThread.mainLoop(Unknown Source)
at java.util.TimerThread.run(Unknown Source)
Caused by: com.zimbra.common.service.ServiceException: system failure: Synchronization of folder '/Inbox' failed
ExceptionId:sync-mbox-davidbz@ymail.com:1366208655221:df940fee6cc603ae
Code:service.FAILURE
at com.zimbra.common.service.ServiceException.FAILURE (ServiceException.java:253)
at com.zimbra.cs.datasource.imap.ImapSync.syncFailed( ImapSync.java:388)
at com.zimbra.cs.datasource.imap.ImapSync.syncMessage s(ImapSync.java:329)
at com.zimbra.cs.datasource.imap.ImapSync.syncFolders (ImapSync.java:239)
at com.zimbra.cs.datasource.imap.ImapSync.importData( ImapSync.java:164)
... 11 more
Caused by: com.zimbra.common.service.ServiceException: system failure: Error while fetching message for UID 1186
ExceptionId:sync-mbox-davidbz@ymail.com:1366208655221:df940fee6cc603ae
Code:service.FAILURE
at com.zimbra.common.service.ServiceException.FAILURE (ServiceException.java:253)
at com.zimbra.cs.datasource.imap.ImapFolderSync.check CanContinue(ImapFolderSync.java:1195)
at com.zimbra.cs.datasource.imap.ImapFolderSync.fetch Messages(ImapFolderSync.java:862)
at com.zimbra.cs.datasource.imap.ImapFolderSync.fetch Messages(ImapFolderSync.java:750)
at com.zimbra.cs.datasource.imap.ImapFolderSync.syncM essages(ImapFolderSync.java:346)
at com.zimbra.cs.datasource.imap.ImapSync.syncMessage s(ImapSync.java:326)
... 13 more
Caused by: com.zimbra.cs.mailclient.MailException: Unexpected tag in response(expected C08 but got C07)
at com.zimbra.cs.mailclient.imap.ImapRequest.checkSta tus(ImapRequest.java:121)
at com.zimbra.cs.mailclient.imap.ImapRequest.sendChec kStatus(ImapRequest.java:112)
at com.zimbra.cs.mailclient.imap.ImapConnection.uidFe tch(ImapConnection.java:331)
at com.zimbra.cs.mailclient.imap.ImapConnection.uidFe tch(ImapConnection.java:379)
at com.zimbra.cs.mailclient.imap.ImapConnection.uidFe tch(ImapConnection.java:397)
at com.zimbra.cs.datasource.imap.ImapFolderSync.fetch Messages(ImapFolderSync.java:854)
... 16 more

If issue persists please post description and debug information here.
Send Error Report