Please help. The server was functioning just fine for 4 weeks. Both errors were solved after re-indexing the mailboxes. What is the probability for the 2 errors to re-appear and what preventive measures/fixes should be done?

Server Configuration
Debian 3.1

1. Cannot receive message, all mailboxes affected
451 4.0.0 Temporary message delivery failure try again (in reply to end of data command)

2. Cannot send message (1 mailbox affected). Re-indexing mailbox partially resoved this problem.

msg - system failure: indexMessage caught IOException
com.zimbra.cs.service.ServiceException: system failure: indexMessage caught IOException
at com.zimbra.cs.service.ServiceException.FAILURE(Ser viceException.java:174)
at com.zimbra.cs.index.Indexer.indexMessage(Indexer.j ava:161)
at com.zimbra.cs.mailbox.Message.reindex(Message.java :421)
at com.zimbra.cs.mailbox.Mailbox.endTransaction(Mailb ox.java:4371)
at com.zimbra.cs.mailbox.Mailbox.addMessageInternal(M ailbox.java:3318)
at com.zimbra.cs.mailbox.Mailbox.addMessage(Mailbox.j ava:3062)
at com.zimbra.cs.mailbox.Mailbox.addMessage(Mailbox.j ava:3034)
at com.zimbra.cs.mailbox.MailSender.sendMimeMessage(M ailSender.java:183)
at com.zimbra.cs.mailbox.MailSender.sendMimeMessage(M ailSender.java:119)
at com.zimbra.cs.operation.SendMsgOperation.callback( SendMsgOperation.java:73)
at com.zimbra.cs.operation.Operation.schedule(Operati on.java:190)
at com.zimbra.cs.service.mail.SendMsg.handle(SendMsg. java:109)
at com.zimbra.soap.SoapEngine.dispatchRequest(SoapEng ine.java:261)
at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.jav a:162)
at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.jav a:84)
at com.zimbra.soap.SoapServlet.doPost(SoapServlet.jav a:223)
at javax.servlet.http.HttpServlet.service(HttpServlet .java:709)
at com.zimbra.cs.servlet.ZimbraServlet.service(Zimbra Servlet.java:173)
at javax.servlet.http.HttpServlet.service(HttpServlet .java:802)
at org.apache.catalina.core.ApplicationFilterChain.in ternalDoFilter(ApplicationFilterChain.java:252)
at org.apache.catalina.core.ApplicationFilterChain.do Filter(ApplicationFilterChain.java:173)
at org.apache.catalina.core.StandardWrapperValve.invo ke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invo ke(StandardContextValve.java:178)
at org.apache.catalina.core.StandardHostValve.invoke( StandardHostValve.java:126)
at org.apache.catalina.valves.ErrorReportValve.invoke (ErrorReportValve.java:105)
at org.apache.catalina.core.StandardEngineValve.invok e(StandardEngineValve.java:107)
at org.apache.catalina.valves.AccessLogValve.invoke(A ccessLogValve.java:541)
at org.apache.catalina.connector.CoyoteAdapter.servic e(CoyoteAdapter.java:148)
at org.apache.coyote.http11.Http11Processor.process(H ttp11Processor.java:869)
at org.apache.coyote.http11.Http11BaseProtocol$Http11 ConnectionHandler.processConnection(Http11BaseProt ocol.java:667)
at org.apache.tomcat.util.net.PoolTcpEndpoint.process Socket(PoolTcpEndpoint.java:527)
at org.apache.tomcat.util.net.LeaderFollowerWorkerThr ead.runIt(LeaderFollowerWorkerThread.java:80)
at org.apache.tomcat.util.threads.ThreadPool$ControlR unnable.run(ThreadPool.java:684)
at java.lang.Thread.run(Thread.java:595)
Caused by: java.io.IOException: Could not create index /opt/zimbra/index/0/12/index/0 (directory already exists)
at com.zimbra.cs.index.MailboxIndex.openIndexWriter(M ailboxIndex.java:906)
at com.zimbra.cs.index.MailboxIndex.addDocument(Mailb oxIndex.java:349)
at com.zimbra.cs.index.Indexer.addDocument(Indexer.ja va:354)
at com.zimbra.cs.index.Indexer.addDocument(Indexer.ja va:324)
at com.zimbra.cs.index.Indexer.indexMessage(Indexer.j ava:156)
... 32 more
Caused by: java.io.IOException: Lock obtain timed out: Lock@/opt/zimbra/apache-tomcat-5.5.1...3c7-write.lock
at org.apache.lucene.store.Lock.obtain(Lock.java:58)
at org.apache.lucene.index.IndexWriter.<init>(IndexWr iter.java:223)
at org.apache.lucene.index.IndexWriter.<init>(IndexWr iter.java:173)
at com.zimbra.cs.index.MailboxIndex.openIndexWriter(M ailboxIndex.java:887)
... 36 more

code - service.FAILURE
method - ZmCsfeCommand.prototype.invoke
detail - soap:Receiver