Searched, tried and still doesn't solve the issue.
An object with that name already exists.
method: [unknown]
msg: object with that id already exists: 4720
code: mail.ALREADY_EXISTS
detail: soap:Sender
trace: com.zimbra.cs.mailbox.MailServiceException: object with that id already exists: 4720 ExceptionId:btpool0-2://mail.ssis.asia/service/soap/SaveDraftRequest:1313884444964:67f095beb36b1ce8 Code:mail.ALREADY_EXISTS Arg

itemId, IID, "4720") at com.zimbra.cs.mailbox.MailServiceException.ALREADY _EXISTS(MailServiceException.java:395) at com.zimbra.cs.db.DbMailItem.create(DbMailItem.java :207) at com.zimbra.cs.mailbox.Message.createInternal(Messa ge.java:533) at com.zimbra.cs.mailbox.Message.create(Message.java: 461) at com.zimbra.cs.mailbox.Mailbox.addMessageInternal(M ailbox.java:4925) at com.zimbra.cs.mailbox.Mailbox.addMessage(Mailbox.j ava:4736) at com.zimbra.cs.mailbox.Mailbox.saveDraftInternal(Ma ilbox.java:5132) at com.zimbra.cs.mailbox.Mailbox.saveDraft(Mailbox.ja va:5120) at com.zimbra.cs.service.mail.SaveDraft.handle(SaveDr aft.java:126) at com.zimbra.soap.SoapEngine.dispatchRequest(SoapEng ine.java:412) at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.jav a:287) at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.jav a:158) at com.zimbra.soap.SoapServlet.doWork(SoapServlet.jav a:294) at com.zimbra.soap.SoapServlet.doPost(SoapServlet.jav a:215) at javax.servlet.http.HttpServlet.service(HttpServlet .java:725) at com.zimbra.cs.servlet.ZimbraServlet.service(Zimbra Servlet.java:208) at javax.servlet.http.HttpServlet.service(HttpServlet .java:814) at org.mortbay.jetty.servlet.ServletHolder.handle(Ser vletHolder.java:511) at org.mortbay.jetty.servlet.ServletHandler$CachedCha in.doFilter(ServletHandler.java:1166) at com.zimbra.cs.servlet.SetHeaderFilter.doFilter(Set HeaderFilter.java:79) at org.mortbay.jetty.servlet.ServletHandler$CachedCha in.doFilter(ServletHandler.java:1157) at org.mortbay.servlet.UserAgentFilter.doFilter(UserA gentFilter.java:81) at org.mortbay.servlet.GzipFilter.doFilter(GzipFilter .java:132) at org.mortbay.jetty.servlet.ServletHandler$CachedCha in.doFilter(ServletHandler.java:1157) at org.mortbay.jetty.servlet.ServletHandler.handle(Se rvletHandler.java:388) at org.mortbay.jetty.security.SecurityHandler.handle( SecurityHandler.java:218) at org.mortbay.jetty.servlet.SessionHandler.handle(Se ssionHandler.java:182) at org.mortbay.jetty.handler.ContextHandler.handle(Co ntextHandler.java:765) at org.mortbay.jetty.webapp.WebAppContext.handle(WebA ppContext.java:422) at org.mortbay.jetty.handler.ContextHandlerCollection .handle(ContextHandlerCollection.java:230) at org.mortbay.jetty.handler.HandlerCollection.handle (HandlerCollection.java:114) at org.mortbay.jetty.handler.HandlerWrapper.handle(Ha ndlerWrapper.java:152) at org.mortbay.jetty.handler.rewrite.RewriteHandler.h andle(RewriteHandler.java:230) at org.mortbay.jetty.handler.HandlerWrapper.handle(Ha ndlerWrapper.java:152) at org.mortbay.jetty.handler.DebugHandler.handle(Debu gHandler.java:77) at org.mortbay.jetty.handler.HandlerWrapper.handle(Ha ndlerWrapper.java:152) at org.mortbay.jetty.Server.handle(Server.java:326) at org.mortbay.jetty.HttpConnection.handleRequest(Htt pConnection.java:543) at org.mortbay.jetty.HttpConnection$RequestHandler.co ntent(HttpConnection.java:946) at org.mortbay.jetty.HttpParser.parseNext(HttpParser. java:756) at org.mortbay.jetty.HttpParser.parseAvailable(HttpPa rser.java:218) at org.mortbay.jetty.HttpConnection.handle(HttpConnec tion.java:405) at org.mortbay.io.nio.SelectChannelEndPoint.run(Selec tChannelEndPoint.java:410) at org.mortbay.thread.BoundedThreadPool$PoolThread.ru n(BoundedThreadPool.java:451) Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityCons traintViolationException: Duplicate entry '306-4720' for key 'PRIMARY' Query being executed when exception was thrown: INSERT INTO mboxgroup6.mail_item(mailbox_id, id, type, parent_id, folder_id, index_id, imap_id, date, size, volume_id, blob_digest, unread, flags, tags, sender, subject, name, metadata, mod_metadata, change_date, mod_content) VALUES (306, 4720, 5, null, 6, 4720, 4720, 1313884444, 668, '1', 'RTo8DLJjKUvnFW6jJxvCkcpn7e0=', 0, 65, 0, 'Yumi You Jia (游嘉)', 'Test', null, 'd1:dd3:asti0e4:idnt36:055d8e7d-41c8-4164-8f64-925c6229b134e1:f9:Test Mail1:s61:Yumi You Jia =?utf-8?B?KOa4uOWYiSk=?= 1:t37:Tan Yong Tin 1:vi10ee', 14505, 1313884444, 14505) at sun.reflect.NativeConstructorAccessorImpl.newInsta nce0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInsta nce(NativeConstructorAccessorImpl.java:39) at sun.reflect.DelegatingConstructorAccessorImpl.newI nstance(DelegatingConstructorAccessorImpl.java:27) at java.lang.reflect.Constructor.newInstance(Construc tor.java:513) at com.mysql.jdbc.Util.handleNewInstance(Util.java:40 9) at com.mysql.jdbc.Util.getInstance(Util.java:384) at com.mysql.jdbc.SQLError.createSQLException(SQLErro r.java:1041) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.ja va:3566) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.ja va:3498) at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:19 59) at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java :2113) at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionIm pl.java:2568) at com.mysql.jdbc.PreparedStatement.executeInternal(P reparedStatement.java:2113) at com.mysql.jdbc.PreparedStatement.executeUpdate(Pre paredStatement.java:2409) at com.mysql.jdbc.PreparedStatement.executeUpdate(Pre paredStatement.java:2327) at com.mysql.jdbc.PreparedStatement.executeUpdate(Pre paredStatement.java:2312) at com.zimbra.cs.db.DebugPreparedStatement.executeUpd ate(DebugPreparedStatement.java:169) at org.apache.commons.dbcp.DelegatingPreparedStatemen t.executeUpdate(DelegatingPreparedStatement.java:1 05) at org.apache.commons.dbcp.DelegatingPreparedStatemen t.executeUpdate(DelegatingPreparedStatement.java:1 05) at com.zimbra.cs.db.DbMailItem.create(DbMailItem.java :192) ... 42 more