I have a server (550 clients in a 3.5 gb machine, 4.5.5GA) that hangs every 2 hours.

mailbox.log starts giving this errors:

2007-06-26 08:16:23,156 INFO [Pop3Server-268] [] ProtocolHandler - Exception oc
curred while handling connection
java.net.SocketException: Connection reset
at java.net.SocketOutputStream.socketWrite(SocketOutp utStream.java:96)
at java.net.SocketOutputStream.write(SocketOutputStre am.java:136)
at java.io.BufferedOutputStream.flushBuffer(BufferedO utputStream.java:65
at java.io.BufferedOutputStream.write(BufferedOutputS tream.java:78)
at com.zimbra.cs.pop3.Pop3Handler.sendMessage(Pop3Han dler.java:429)
at com.zimbra.cs.pop3.Pop3Handler.doRETR(Pop3Handler. java:625)
at com.zimbra.cs.pop3.Pop3Handler.processCommandInter nal(Pop3Handler.jav
at com.zimbra.cs.pop3.Pop3Handler.processCommand(Pop3 Handler.java:141)
at com.zimbra.cs.tcpserver.ProtocolHandler.processCon nection(ProtocolHan
at com.zimbra.cs.tcpserver.ProtocolHandler.run(Protoc olHandler.java:198)
at EDU.oswego.cs.dl.util.concurrent.PooledExecutor$Wo rker.run(Unknown So
at java.lang.Thread.run(Thread.java:595)
2007-06-26 08:16:23,156 INFO [Pop3Server-268] [] ProtocolHandler - Handler exit
ing normally

And after 3 or 4 of these, this start to appear:

2007-06-26 08:16:48,535 WARN [Pop3Server-591] [ip=;] sqltrace - Conn
ection pool is 75% utilized. 8 connections out of a maximum of 10 in use. Turn
on debug logging for zimbra.sqltrace to see stack traces of connections not ret
urned to the pool.

2 minutes later, tomcat hangs and all connections get answered, but no output appears.

tomcat stop; tomcat start fixes it for another couple of hours...

Any way to trace whats happening? The problem started after a controlled reboot to move the machine to another rack.